Autologous LCL Research Articles

A Novel Strategy to Render CTL Resistant to Immunosuppression with Calcineurin Inhibitors

EBV-associated Post Transplant Lymphoproliferative Disease (PTLD) is a major complication of solid organ transplantation (SOT), arising from suppression of normal EBV-specific T-cell responses by immunosuppressive drugs, chiefly the calcineurin inhibitors Cyclosporin (CsA) and Tacrolimus (FK506). Previous studies in the SCT setting have established that adoptive immunotherapy with EBV-specific cytotoxic T-cells (CTL) is highly effective in preventing/treating PTLD, but results with this approach in the SOT setting have been less impressive, reflecting the ongoing need for immunosuppression to prevent rejection in SOT patients. We have addressed the critical issue of how to enable infused CTL to proliferate and function in the face of immunosuppression with calcineurin inhibitors. We report the generation of Calcineurin A (CnA) and Calcineurin B (CnB) mutants which render CTL resistant to CsA and FK506.Based on structural data, we designed 22 CnA mutants and 32 CnB mutants predicted to dephosphorylate NFAT but not to bind to FKBP12-FK506/cyclophilin-CsA. Using transient assays with an NFAT-luciferase reporter in PMA/ionomycin stimulated 293T cells, we identified 6 CnA/4 CnB mutants which gave >15% resistance to FK506, and 5 CnA/5CnB mutants giving resistance to CsA. 4 CnB mutants resulted in resistance to both FK506 and CsA. Transduction of Jurkat T-cells with retroviral vectors coding for these Cn mutants resulted in high level expression, as determined by Western blotting/flow cytometry. The ability of these mutants to confer resistance to FK506 and CsA in Jurkat cells was then determined by measuring IL-2 secretion in response to PMA/ionomycin stimulation, in the presence of increasing concentrations of immunosuppressive drugs. Resistance was found to correlate well with that seen in 293T cells. Significantly, mutants CnA12 and B30 enabled equivalent secretion of IL-2 to untransduced Jurkats without immunosuppression despite supra-therapeutic doses of FK506 (40ng/ml) and likewise CnA22 and B30 despite supra-therapeutic CsA (800ng/ml). Some mutants rendered Jurkat T-cells more responsive to stimulation with increased output of IL-2 in the absence of IS. Next, EBV-CTLs from normal donors were retrovirally transduced with the 3 Cn mutants shown to confer greatest resistance in the Jurkat IL-2 secretion assay. In the absence of Cn inhibitors, the proportion of transduced cells, as determined by eGFP positivity, remained constant throughout subsequent culture. In contrast, in the presence of CsA/FK506, the proportion of transduced cells increased from a mean of 60% to >90% after 3 stimulations with autologous LCLs, demonstrating a selective advantage for transduced CTL. More importantly, transduced CTL were able to proliferate in response to stimulation with autologous LCL in the presence of immunosuppression, whereas non-transduced cells did not expand with FK506 or CsA. As shown in Fig 1, CTLs transduced with CnB30 proliferated at a comparable rate in the face of either FK506 (mean 30-fold expansion after 3 stimulations) or CsA (mean 47-fold expansion) to untransduced CTL not exposed to Cn inhibitors (mean 50 fold). CTL transduced with CnA22 were resistant to CsA whilst remaining sensitive to FK506. Further, transduced CTL secreted normal levels of IFN-g following stimulation with LCL in the presence of either FK506 or CsA: (CnB30 transduced CTL mean 1485 pg/ml IFN-g without immunosuppression, 1563 pg/ml in 10 ng/ml FK506 and 1600 pg/ml in 200 ng/ml CsA). In contrast, IFN-g secretion from untransduced CTL was abrogated by these drugs (mean 1538 pg/ml IFN-g without immunosuppression and 0 pg/ml with either FK506 or CsA).In summary, we have developed a strategy that effectively renders EBV-CTLs resistant to either FK506 or CsA. Potentially this may be of significant benefit to SOT patients developing PTLD, by allowing effective immunotherapy with EBV CTL without the need for reduction of calcineurin inhibitors and the attendant risk of graft rejection. More broadly, this may represent a generic approach to enabling adoptively transferred T-cells function in the face of ongoing immunosuppression. [Display omitted]

Generation of Epstein Barr Virus Specific Cytotoxic T Lymphocytes (EBVCTLs) Resistant to the Immunosuppressive Drug Tacrolimus (FK506)

Adoptive transfer of autologous EBV-CTLs to hematopoietic stem cell transplant (HSCT) and solid organ transplant (SOT) recipients is a safe and often effective means for prevention and treatment of EBV-associated post transplant lymphoproliferative disorders (PTLD). Although immunosuppressive drugs can be tapered in patients developing PTLD, they often cannot be completely withdrawn because of the risk of graft rejection, a particular concern in lung, heart or liver transplant recipients. These immunosuppressive drugs may limit the expansion, persistence and efficacy of transferred EBV-CTLs. One of the most widely used immunosuppressive agents is FK506 whose effects are highly dependent on binding FKBP12 proteins, since T cells generated from FKBP12 knockout mice are completely resistant to the inhibitory effects of FK506. We have generated EBV-CTLs resistant to FK506 by knocking down FKBP12 using a small interfering RNA (siRNA) stably expressed from a retroviral vector. After extensively screening potential target sequences, we identified one, designed as siRNA4, that knocks down >90% of FKBP12 protein expression in T cell lines and also in EBV-CTLs, as assessed by Western blotting. We then generated two retroviral vector encoding for siRNA4/eGFP and irrelevant siRNA/eGFP, respectively. These vectors were used to transduce established EBV-CTL lines generated from 7 EBV-seropositive donors. Transduction efficiency was 46.3±22.5% and 55.4±27.5% for siRNA4 and irrelevant-siRNA, respectively. We measured the proliferation of transduced CTLs in the presence of FK506, in short term and long term cultures. Using a thymidine uptake assay, we found that the inhibiton of proliferation by increasing concentrations of FK506 was significantly diminished in siRNA4+ CTLs compared to control CTLs (41±4% inhibition for siRNA4+ CTLs vs 74± 2% for control CTLs). To evaluate the effects of knocking down FKBP12 in long-term cultures, control and siRNA4+ CTLs were stimulated weekly with the antigen (autologous EBV-LCL) with or without the addition of FK506 (5ng/ml) and low dose IL-2 (20U/mL). We found that the proportion of siRNA4+ CTLs increased over time not only as a percentage of GFP+ cells (from 46±22% to 89.4±5.3% after 5 stimulations) but also numerically (median fold expansion: 34.3, range 5–60). In contrast, control EBV-CTLs did not show any selection in culture, since the percentage of GFP+ cells remained unchanged (from 56±27% to 57±23.1%) and CTLs ceased to proliferate (median fold expansion: 2, range 0–5). Finally, we found that siRNA4+ CTLs retained their antigen specificity, having MHC-restricted cytotoxic activity against EBV-targets (66±22% vs 16±12% for autologous and allogenic LCL, respectively at an E:T ratio of 20:1 for siRNA4+ CTLs; 61±12% vs 15±12% for autologous and allogenic LCL, respectively, for control CTLs). Modified CTLs also maintained their production of IFNγ in response to specific EBV-peptides, as assessed by ELIspot assays. We are currently evaluating the in vivo expansion of genetically modified EBV-CTLs in the presence of FK506. In conclusion, we have developed a strategy that produces EBV-CTLs resistant to FK506. This strategy may be beneficial to improve EBV immune reconstitution in patients at high risk of developing post transplant lymphoma.

Approach to Establish Long Term Anti-Acute Myeloid Leukemia (AML) Immune Responses by Inducing Central Memory AML Specific CD4 T Cells.

The efficacy of adoptive cell therapy of cancer and leukemia is often limited by the failure of cultured T cells, particularly cloned CD8+ T cells, to persist in vivo, and insight into the basis for the poor survival of the transferred cells is lacking. We previously reported a novel culture method that induces AML dendritic cell differentiation and primes in situ AML-reactive T cells (AMLDC culture) (Zhong et al. Exp Hematol 2008, 36:486). Highly reactive anti-AML T-cell lines were generated. These T-cell lines caused specific lysis of autologous AML cells, but not autologous LCL or allogeneic AML cells, and they depleted autologous AML colony-forming cells (CFC), but not normal CFC. The culture procedure has been further optimized in this study. We found that by the addition of the TLR-4 agonist LPS,(1–100 ng/ml) in the last 24 hours of AMLDC culture (day 6), CD80, CD86, CD53, CD83 or HLA-Dr expression of AML cells pre-induced by cytokine combination GM-CSF/IL-4 or GM-CSF/IL4/IL2/IL7/IL12 could be significantly enhanced (n=6, P<0.005–0.04; n=8, P<0.0001–0.005 respectively). Addition of LPS increased the IFN-gamma secretion by T cells generated from AMLDC culture in response to autologous AML cells 4–10 fold (3 of 3; P<0.001). Addition of TNF-alpha, (10–20 ng/ml) in the last 24 hours of culture could also significantly enhance the expression of above surface molecules. However, LPS induced significantly higher expression of CD80 and CD86 on AMLDC compared with TNF-alpha. T cells generated from AMLDC culture with TNF-alpha led to differential effects on autologous AML reactivity. IFN-gamma secretion was enhanced in 4 of 7 studies and suppressed in 3 of 7. The significantly enhanced AML cell reactivity of autologous T cells generated from AMLDC culture by adding LPS was also demonstrated in limiting dilution AMLDC culture in 96 well plates. The majority of T cell lines selected and expanded from AMLDC culture with LPS were CD3+CD4+ (12 of 18), and 18 T cell lines tested expressed moderate to high level of CD62L, implying the central memory phenotype.Conclusions: Timely exposure of AMLDC culture to TLR-4 agonists, followed by T cell expansion, may promote the generation of AML-reactive T cells and differentiation toward the central memory phenotype. Theoretically, this should promote long-term maintenance and potential of regulation of both humoral and cellular immune responses against AML upon infusion of AML reactive autologous T cells derived from such cultures and may therefore enhance the therapeutic efficacy of these cells.

Rapid Generation of Antigen-Specific T Cells for Pre-Clinical and Clinical Applications Using a Novel Mini Cell Bioreactor

Although flasks, bags, or rocking bioreactors can readily expand T lymphocytes after non-specific stimulation, the requirements for antigen-driven expansion of cytotoxic T lymphocytes (CTLs) are more rigorous. Antigen-specific T cells proliferate optimally only in the 2 mL wells of 24-well plates and cannot reproducibly be adapted to growth in flasks or bags. Hence, preparation of antigen-specific T cells for adoptive immunotherapy of malignancies is extremely time-consuming, requiring between 4wks and 3mths to produce sufficient cells for therapeutic purposes, and expensive (media + plastics + cytokines + man hours). The extensive manipulation required during the culturing process increases the risk of contamination. In combination, these problems obstruct the broader clinical application of antigen-specific T cells. Antigen-specific T cell growth is limited by gas exchange, nutrients and waste buildup. Bioreactors developed to provide these requirements tend to be complex, involving mechanical rocking or stirring and continuous perfusion, which increases the expense of the procedure and limits the number of products to the number of mechanical devices that can be housed and maintained. We have now explored the use of a new static mini Cell Bioreactor for antigen-specific T cell expansion. This device is essentially a flask with a gas permeable membrane supported by a plastic lattice as its base. The O2/CO2 exchange from the base allows large volumes of media to be added thereby reducing nutrient limitations and waste build-up, and consequently the manipulation required to sustain cell expansion. We tested two different sizes of Cell Bioreactor, 10 cm2 and 100 cm2 that hold a maximum of 40mL and 2000mL of media, respectively. We were able to generate and expand Epstein-Barr virus antigen-specific cytotoxic T lymphocytes (EBVCTLs) from normal donors by coculturing antigen presenting cells (APC) (1.4E+05 × cm2) with established EBV-CTL (4.3E+03 × cm2) at an optimized cell density and stimulator: responder ratio (32:1). These culture conditions induced accelerated CTL expansion (42.5 fold ±14.8 vs 3.4 fold ±1.2 within 7 days) without media change. Manipulation was restricted to cytokine addition every 3–4 days and to LCL stimulation on a weekly basis. A single 100cm2 bioreactor could produce up to 800E+06 antigen-specific T cells, which would have required approximately 320 wells in 24 well plates (>13 plates) under standard culture conditions. The CD4:CD8 T cell ratio and phenotype of the Cell Bioreactor-expanded CTLs was similar to those expanded using the conventional method (CD27 48% vs 52.4%, CD28 65.2% vs 62.2%, CD62L 53.15% vs 54.5%, CD45RO 58.1% vs 55.7%, and CD45RA 51.1% vs 54.9%). Antigen specificity, as evaluated by tetramer analysis and IFN-g ELIspot assay demonstrated no significant differences between CTL expanded by each process. Finally, cytolytic function was confirmed using a standard chromium release assay where both sources of CTL had high specific killing of the autologous EBV-transformed LCL targets (85%±12% vs 77%±19%) and minimal killing of allogeneic targets (22%±9% vs 15%±12).In summary, we have successfully utilized the new mini Cell Bioreactor technology to induce optimal in vitro antigen-specific T cell expansion with minimal handling. Future work will evaluate the impact of the accelerated expansion on differentiation and memory markers. This new system is suited to the clinical grade expansion of other cell types including suspension cell lines, and mitogen-activated T cells, as well as T cell blasts engrafted with chimeric antigen receptors.

Engineering Human Tumor-specific Cytotoxic T Cells to Function in a Hypoxic Environment

Hypoxia occurs in many tumors and reduces the effectiveness of radio- and chemotherapy. Hypoxia also impedes immune responses to tumors, reducing T lymphocyte production of cytokines such as interleukin-2 (IL-2) and interferon gamma, as well as the survival and proliferation of these cells. We constructed a lentiviral vector encoding a bidirectional hypoxia-inducible responsive element (HRE) derived from human vascular endothelial growth factor, which drives the hIL-2 gene and a marker gene. We used a model of human B cell lymphoma to show that tumor-specific T cells modified with this vector upregulate hIL-2 expression when oxygen tension is low in vitro and in vivo. The consequence of this effect is to increase T-cell survival and proliferation whilst sustaining effector function, even in O(2) concentrations as low as 1%. The phenotype of the transduced cells is unchanged, as is their ability to migrate to tumor. HRE-IL-2-modified cytotoxic T lymphocytes (CTLs) produce faster and more complete tumor regression than parental CTLs and increase overall survival. Hypoxia-resistant T cells may thus be of value in the treatment of human tumors in which areas of hypoxia may otherwise account for resistance to this therapeutic strategy.

Generation of T-cell lines to autologous acute myeloid leukemia cells by competitive limiting dilution culture of acute myeloid leukemia mononuclear cells

To develop a novel method of generating multiple autologous acute myeloid leukemia (AML) reactive T-cell lines as a step toward adoptive immunotherapy for AML. AML peripheral blood mononuclear cells (MNC), including >90% AML blasts and 1% to 3% T cells, were seeded in limiting dilution culture in which AML blasts were induced to undergo dendritic cell (DC) differentiation. T cells were primed and activated with the addition of a cytokine combination. Highly reactive anti-AML T-cell lines (both CD4(+) and CD8(+)) were generated, selected, and expanded. The estimated average frequency of AML-reactive T cells or precursors was 6 +/- 3/1,000,000 AML peripheral blood mononuclear cells (n = 11). Robust intracellular interferon-gamma (IFN-gamma) release from T-cell lines was demonstrated by flow cytometry after stimulation by autologous AML cells, but not an autologous B-lymphoblastoid cell line (LCL). These T-cell lines caused specific lysis of autologous AML cells, but not autologous LCL or allogeneic AML cells, and they depleted autologous AML colony-forming cells (CFC), but not normal CFC. Most CD4(+) T-cell lines exerted strong proapoptotic effects on AML cells. AML cell apoptosis by CD4(+) T-cell lines correlated with IFN-gamma secretion. This study demonstrates a methodology for generating large numbers of AML-reactive cytotoxic T cell lines (either class I or II restricted) that may be useful clinically in adoptive immunotherapy. This study also provides estimates of AML-reactive T-cell frequency in patients with AML.

Direct Genotyping of Coding Non-Synonymous SNPs for Identification of Novel Minor Histocompatibility Antigens.

Traditional methods for identifying minor histocompatibility antigens (mHags) are technically challenging and biased against discovery of mHags not expressed in the peripheral blood. In this work, we propose a rapid, unbiased, genetic approach for identification minor antigens resulting from disparities in coding non-synonymous SNPs (“C SNPS”). This approach is capable of testing for responses to candidate minor antigens expressed in virtually any tissue, including those expressed exclusively in tissues targeted by GVHD. The first step in our approach begins with comparison of donor and recipient C SNP genotypes generated using C SNP microarrays. These arrays interrogate approximately 80% of human C SNPs predicted to occur in greater than 5% of the population. Comparison of C SNP genotypes directly identifies protein-altering alleles present in the recipient but not the donor (hereafter referred to as “recipient-restricted” alleles), thereby identifying a transplant-specific set of candidate minor antigens. The second step utilizes conventional HLA-class I epitope prediction performed on all linear peptides that include amino-acid residues defined by a recipient-restricted allele. This two step filtering process identifies a small, “testable” number candidate minor peptide epitopes for an individual expressed HLA-class I allele. Candidate epitopes can then be synthesized, pooled and tested at diagnosis of GVHD using a commercial Granzyme B ELISPOT assay. As proof-of-principal for a direct genotyping approach, we have analyzed C SNP genotypes, performed epitope prediction and generated T-cell lines specific for candidate minor antigens using DNA and PBL from a pair of disease-free HLA-identical siblings. Analysis of 10,000 C SNPs shows that approximately 2,000 C SNP alleles are restricted to one sibling within the pair. BIMAS epitope prediction of short unique peptide sequences determined by each sibling-restricted allele identifies approximately 100 candidate minor epitopes predicted to bind HLA-A*0201. These candidate minor epitopes were ranked using expression microarrays performed on EBV-transformed LCL derived from each sibling, with candidates derived from highly expressed genes ranked above those from genes with lower expression levels. A pool of 12 candidate minor epitopes that were both unique to sibling “A” and derived from genes highly expressed in LCL were synthesized and used to generate CD8+ T-cell lines from sibling “B”. Stimulation utilized autologous (sibling “B”-derived) mature dendritic cells loaded with candidate minor epitopes. After several rounds of in-vitro stimulation, each T-cell line was tested for responses to EBV-LCL from sibling “B” and sibling “A” using a Granzyme B ELISPOT kit. Five out of sixteen lines responded to LCL from sibling A while no line responded to autologous LCL. Thus we show that this approach frequently generates CD8+ T-cell lines specific for sibling-derived target cells, suggesting that this approach efficiently identifies genuine, novel, endogenously processed and presented minor epitopes. Deconvolution of the peptide pool suggests that at least two out of the twelve candidate minor epitopes are naturally processed and presented.

Generation of Acute Myeloid Leukemia (AML)-Specific Autologous CD4 and CD8 T Cell Lines by Limiting Dilution AML Dendritic Cell Culture.

Naturally occurring cytotoxic T cells directed against various leukemia associated antigens (LAA) expressed by acute myeloid leukemia (AML) cells have been described. However, these LAA-specific T cells are rare and obviously unable to initiate effective anti-leukemia responses. The challenge is how to investigate, select, activate and expand the rare LAA-specific T cells from the vast population of blood cells in patients with AML for immunotherapy. Based on our studies of inducing AML dendritic cell (AMLDC) differentiation and priming in situ AML-reactive T cells, we have developed a novel method of generating multiple autologous AML reactive T cell lines by limiting dilution AMLDC (LD-AMLDC) culture. The principle of LD-AMLDC is based on the assumption that autologous AML-reactive T cells or precursors are randomly distributed in the AML PBMC suspension, and that each one has an equal opportunity to respond to AML cells in the 96-well plates under optimized culture condition. By culturing AML PBMC (&gt;90% blasts) in culture medium supplemented with GM-CSF/IL4/IL2/IL7/IL12 to induce AML DC differentiation and activate in situ autologous T cells, highly reactive anti-AML T cell lines (both CD4+ and CD8+ lines) were selected and expanded from LD-AMLDC culture using the appropriate numbers of AML PBMC in each culture well by the criterion of release of IFN-gamma in response to autologous AML blasts. By maximum likelihood solution, the estimated average frequency of AML reactive T cells or precursors is 6±3/1,000,000 AML PBMC (n=8). Strong intracellular IFN-gamma release of T cell lines obtained in LD-AMLDC was demonstrated by flow cytometry analysis after stimulation by autologous AML cells but not autologous B-lymphoblastoid cell line (LCL) (Figure). Effective specific lysis (up to 70% at E:T=20:1) of autologous AML cells but not autologous LCL or allogeneic AML cells by these T cell lines was observed. Two PR1 specific T cell lines were obtained by screening 39 AML reactive HLA-A2+ CD8+ T cell lines generated from 5 LD-AMLDC cultures, suggesting that other unidentified CD4 or CD8 lines with strong autologous AML responses may be reactive to known or unknown LAAs. These results encourage continued efforts to induce, activate and select T cells lines with high autologous AML reactivity using LD-AMLDC culture and to expand multi-LAA reactive T cell lines acquired from limiting dilution AML-DC culture for AML immunotherapy. Figure Figure

Long-Term Preservation of Antibody-Dependent Cellular Cytotoxicity (ADCC) of Natural Killer Cells Amplified In Vitro From the Peripheral Blood of Breast Cancer Patients After Chemotherapy

Twenty percent of breast cancer adenocarcinomas overexpress the oncogene c-erb-2 that is recognized by the humanized anti-Her2/neu monoclonal antibody Herceptin. Results from clinical studies suggest that antibody-dependent cellular cytotoxicity (ADCC) is involved in the clinical response of Herceptin-treated patients. The purpose of the current study was to evaluate the possibility of amplifying in vitro the CD3-/CD16+ natural killer (NK) cell subset that mediates ADCC from breast cancer patients after chemotherapy. Peripheral blood mononuclear cells from six breast cancer patients taken 2 months after chemotherapy completion were co-cultured with an autologous irradiated Epstein-Barr virus-transformed B-lymphoblastoid cell line (LCL) in the presence of interleukin-2 (IL-2) for 4-6 weeks. These LCL + IL2 activated cultures (ACs) were tested for ADCC potential, and their CD3/CD16 NK proportion was quantified. Among the ACs, the proportion of CD3-/CD16+ NK cells increased up to 64% over the first 2 weeks of culture and the ACs continued to expand for 1 month thereafter. Control and patient ACs displayed ADCC activity (tested in the presence of Rituximab against the autologous LCL to take into account any possible effect of inhibitory NK receptors) as well as against the MCF-7(Her2/neu) breast cancer cell line in the presence of Herceptin. This ADCC activity was maintained during the entire culture period. In conclusion, chemotherapy in breast cancer patients does not obviate the possibility of amplifying in vitro the NK cell subset that mediates ADCC. Consequently, adoptive transfer of lymphocytes mediating ADCC can be considered using this protocol to test its benefit in patients under Herceptin treatment.

Functional CD4+ and CD8+ T-Cell Responses Induced by Autologous Mitomycin C Treated Epstein–Barr Virus Transformed Lymphoblastoid Cell Lines

Epstein–Barr virus (EBV) gene expression in tumor cells of posttransplant lymphoproliferative disorder (PTLD) patients resembles that of EBV transformed B-cell lines (LCL). EBV-specific cytotoxic T-lymphocytes can be generated by stimulating peripheral blood lymphocytes with autologous LCL. We describe a standardized method for the growth inactivation and cryopreservation of LCL for optimal T-cell stimulation and analyzed the function and phenotype of responding T-cells. LCL growth was completely blocked by mitomycin C treatment (McLCL) and McLCL could be cryopreserved while retaining excellent APC function. McLCL stimulated both CD4+ and CD8+ T-cells as measured by HLA-DR and CD25 expression using FACS analysis. EBV-specific CTL activity and T-cell proliferation were induced and immunocytochemical staining showed CD4+ and (granzyme B positive) CD8+ T-cells rosetting with McLCL. Granzymes A and B, IFN-γ, and IL-6 were detected at significant levels in the supernatant. Thus, ex vivo T-cell activation with cryopreserved McLCL results in activation of both CD4+ and CD8+ T-cells producing a Th1-like cytokine profile, making this a suitable protocol for adoptive therapy of PTLD.

Suppression of Burkitt's lymphoma tumorigenicity in nude mice by co-inoculation of EBV-immortalized lymphoblastoid cells.

EBV-immortalized B-lymphoblastoid cell lines (LCL) inoculated s.c. into T-cell-deficient nude mice regress completely after a short initial growth period. We tested whether the putative host response underlying this phenomenon might also be directed against progressively growing Burkitt's lymphoma (BL) tumors in nude mice. Outgrowth of BL tumors was suppressed when cells of the highly tumorigenic BL cell line BL 60 were mixed with cells of the autologous LCL IARC 277 before s.c. inoculation into nude mice. Even when the cells were inoculated separately and simultaneously into contralateral flanks of the mice, regression of initially growing BL tumors could be observed, albeit with reduced frequency and dependent on the dose of LCL cells. Tumor growth of BL 60 cells could also be suppressed by co-inoculation with the non-autologous LCL IARC 174 and IARC 277 cells could suppress growth of the non-autologous BL cell line Eli. Pronounced infiltration with murine (m)CD-11b-positive mouse macrophages and mCD-8a-positive mouse lymphoid cells, most probably natural killer cells, was seen in histological tissue sections of regressing BL 60 tumors when LCL cells were inoculated contralaterally. In regressing BL tumors, these mouse cells were present not only in necrotic areas but also in vital BL tissue, indicating that infiltration of mouse cells had taken place before the development of necrosis. Since tumor-infiltrating mouse cells can be activated at least by some human cytokines, we measured cytokine production of BL 60 and IARC 277. High amounts of IL 6 and IL 10 were produced by the LCL cells, whereas IL-6 and IL-10 production by the BL 60 cells was beyond or close to the detection threshold. In addition, IL 8 was secreted up to 5-fold more by the LCL than by the BL cells. The results presented here thus suggest a host response of the nude mouse, which is triggered by cytokines released from the LCL but, once induced, is directed also against BL cells.

Melanoma cells and normal melanocytes share antigens recognized by HLA-A2-restricted cytotoxic T cell clones from melanoma patients.

HLA-A2-restricted, CD3+, CD8+, alpha/beta+ cytotoxic T cell (CTL) clones were isolated from peripheral blood (PBL) or tumor infiltrating lymphocytes (TIL) of two HLA-A2+ melanoma patients (9742 and 5810), to evaluate the possible recognition of autologous melanoma and of allogeneic HLA-A2-matched normal melanocytes. These CTL clones lysed not only fresh and cultured autologous melanoma cells, but also allogeneic HLA-A2+, but not HLA-A2-, normal melanocytes. The lysis of autologous neoplastic cells and of melanocytes could be inhibited by an anti-HLA-A2 monoclonal antibody (mAb). Lysis of the normal melanocytes was not dependent on the presence of human or fetal calf serum in the culture medium. HLA-A2-restricted CTL clones recognized not only proliferating melanocytes cultured in complete melanocyte medium, but also melanocytes made quiescent by culture for up to 6 d in a basal medium devoid of exogenous factors such as phorbol ester (O-tetradecanoyl phorbol 13-acetate [TPA]), epidermal growth factor, insulin, and pituitary extracts. Analysis of specificity of four CTL clones (A75, A83, A94, and 119) from patient 9742, performed on a panel of 39 targets, indicated that the three HLA-A2-restricted CTL (A75, A83, and A94) lysed all but one of nine allogeneic melanomas expressing the HLA-A2 molecule with no reactivity on nine HLA-A2- allogeneic melanomas. Only a few instances of borderline reactivity were seen by the same effectors on 21 targets of nonmelanocyte lineage, including 12 carcinomas of different histology, four Epstein-Barr virus-transformed B cells (lymphoblastoid cell lines [LCL]), including the autologous LCL, four lines of normal fibroblasts, and normal kidney cells. Lack of reactivity on allogeneic targets of nonmelanocyte lineage occurred in spite of expression of HLA-A2 on 14 of these targets as determined by conventional tissue typing and cytofluorimetric analysis with four different anti-HLA-A2 mAb. These data indicate that tissue-related antigens can be expressed on normal and neoplastic cells of the melanocyte lineage and can be recognized in association with HLA-A2 by CTL clones from melanoma patients.

Human CD4 Lymphocytes Specifically Recognize a Peptide Representing the Fusion Region of the Hybrid Protein pml/RARa Present in Acute Promyelocytic Leukemia Cells

Fusion proteins present in leukemic cells frequently contain a new amino acid at the fusion point. We tested whether a peptide (BCR1/25) encompassing the fusion region of the hybrid molecule pml/RAR alpha, which is selectively expressed by acute promyelocytic leukemia (APL) cells, can be recognized by human T lymphocytes in vitro. CD4+ lymphocytes, at both polyclonal and clonal level, recognized peptide BCR1/25 in an HLA-DR--restricted fashion on presentation by autologous antigen-presenting cell (APC) or by APC expressing the HLA-DR11 restricting molecule. Control peptides corresponding to the normal pml and RAR alpha proteins were not recognized. One clone (DEG5) also exerted a high and specific cytotoxicity against autologous cells pulsed with BCR1/25. The autologous DE LCL containing a transduced pml/RAR alpha fusion gene and expressing a bcr1 type of the pml/RAR alpha hybrid protein induced the proliferation of DE anti-BCR1/25 T cell clones. It is concluded that the bcr1 type-pml/RAR alpha fusion protein of APL contains an antigenic site, absent from the normal parent molecules and recognized by human CD4+ lymphocytes.

Human CD4 lymphocytes specifically recognize a peptide representing the fusion region of the hybrid protein pml/RAR alpha present in acute promyelocytic leukemia cells

Fusion proteins present in leukemic cells frequently contain a new amino acid at the fusion point. We tested whether a peptide (BCR1/25) encompassing the fusion region of the hybrid molecule pml/RAR alpha, which is selectively expressed by acute promyelocytic leukemia (APL) cells, can be recognized by human T lymphocytes in vitro. CD4+ lymphocytes, at both polyclonal and clonal level, recognized peptide BCR1/25 in an HLA-DR--restricted fashion on presentation by autologous antigen-presenting cell (APC) or by APC expressing the HLA-DR11 restricting molecule. Control peptides corresponding to the normal pml and RAR alpha proteins were not recognized. One clone (DEG5) also exerted a high and specific cytotoxicity against autologous cells pulsed with BCR1/25. The autologous DE LCL containing a transduced pml/RAR alpha fusion gene and expressing a bcr1 type of the pml/RAR alpha hybrid protein induced the proliferation of DE anti-BCR1/25 T cell clones. It is concluded that the bcr1 type-pml/RAR alpha fusion protein of APL contains an antigenic site, absent from the normal parent molecules and recognized by human CD4+ lymphocytes.

Generation of cytotoxicity with various MHC class I restrictions against autologous LCL by stimulating the lymphocytes with autologous and/or allogeneic LCLs sharing HLA alleles with the responder

We exposed human blood lymphocytes to autologous and to allogeneic lymphoblastoid lines (LCLs), each alone or in combination, and analyzed the MHC Class I restriction pattern of the generated auto-LCL reactive cytotoxicity. In the cultures of two EBV-seropositive, HLA All-positive individuals the majority of cytotoxic lymphocytes generated after repeated stimulation with autologous LCL were restricted by this molecule. One of the cultures was subjected to various stimulation strategies. A relatively low proportion of HLA A2- and HLA B7-restricted cytotoxic T cells could be detected in the autostimulated cultures. Such cells were enriched at the expense of All-restricted ones by stimulating with allogeneic LCLs which lacked HLA All but expressed A2 or B7. Interestingly, stimulation of the lymphocytes with only allogeneic LCL also generated autoreactive CTLs. Thus, by including or using exclusively allogeneic LCL stimulators, the CTL fractions represented by few cells could be enriched.

EBV cell-lines (LCL) and E − cells as stimulator cells for limiting dilution analysis (LDA) of alloreactive IL-2-secreting cells (IL-2-SC) and cytotoxic precursors (CTLp) : Comparison of their stimulator capacity and ability to generate specific alloreactivity

The choice of stimulator cells is crucial in determining the frequency of alloreactive cells by limiting dilution analysis (LDA). In humans, E- cells or EBV-lymphoblastoid cell lines (LCL) are available for this purpose. The E- cells have been mostly used until now, but they appear to stimulate much less than LCL in other models. Consequently, we undertook a systematic comparison of the efficiency of both types of cell for the LDA of alloreactive IL-2-secreting cells (IL-2-SC) and cytotoxic precursors (CTLp). We show that LCL are stronger stimulator cells both for IL-2 secretion and for cytotoxicity induction. However, high levels of non-allogeneic reactivity were also induced. Therefore, to measure the frequency of specific alloreactive IL-2-SC and CTLp, T cells were depleted of such irrelevant reactive cells by a suicide technique: culture with autologous LCL in the presence of BUDR and use of the remaining live cells as responding effectors in LDA. Using this methodology, no non-allogeneic reactive T cells remain in the responding cells: after restimulation by autologous LCL, no IL-2-SC could be seen and no cytotoxic activity could be observed against autologous, irrelevant or LAK sensitive targets. In contrast, the number of IL-2-SC and CTLp against allogeneic targets was preserved. Therefore with this methodology, the strong stimulator capacity of LCL could be used whereas non-specific activation could be avoided in order to assess the frequency of allo-specific IL-2-SC and CTLp.

Defective cell-mediated response to EBV-transformed B cells in a healthy individual with regular EBV antibody titers.

We have analyzed the EBV-related immune parameters of a healthy EBV-seropositive individual (ST) who has regular antibody titers but defective inhibitory capacity toward the growth of autologous EBV-infected B cells. This in vitro function reflects the EBV-specific memory because it does not occur in experiments performed with cells of seronegative individuals. An analysis of events following in vitro EBV infection showed that lymphocytes of ST behaved in some tests in the same way as those collected from seronegative individuals. These parameters were: lack of gamma-IFN production 24 hr after EBV infection; low production of soluble factors that inhibit EBV-induced B-cell proliferation; lack of generation of LCL selective cytotoxicity after repeated stimulation with autologous LCL; and high proportion of EBNA-positive cells in 7-day-old EBV-infected cultures. On the other hand, cellular memory to the virus detected by the production of IL-2 24 hr after infection, and by the production of LIF upon exposure to EBV-encoded antigens, conformed with the results obtained with seropositive individuals. T-cell-mediated inhibition of EBV-induced B-cell growth in vitro has been regarded as a corollary of in vivo control of EBV-infected B cells. However, it is absent or has a low efficiency in certain disease categories which are not accompanied by risk of B-EBV growth. Our results with a healthy individual also indicate that several mechanisms contribute to a harmless life-long virus carrier state.

A human helper-dependent influenza virus-specific cytotoxic T lymphocyte clone restricted by HLA-DR2.

A human influenza A virus-specific cytotoxic T lymphocyte (CTL) clone is described that is restricted by a class II HLA-antigen. Of a large panel of B-lymphoblastoid cell lines (B-LCL) as target cells the clone lysed only infected cells sharing HLA-DR2 with the donor of the clone. In cold target inhibition studies only infected cells bearing HLA-DR2 could inhibit cytotoxicity. Infected PHA-blasts that express less DR-antigen than B-LCL cells were lysed to a much lesser extent though they could be infected equally well. Trypan blue staining and postlabelling of the target cells showed that the clone indeed killed the target cells. The clone did not proliferate in response to infected irradiated autologous LCL cells and had the OKT3+4+8-DR+ phenotype. The possible significance of class II restricted CTL is discussed.

Lymphocyte-mediated lysis of autologous and allogeneic B-cell lines in man

The lytic potential of human blood lymphocytes was assayed against autologous and allogeneic EBV-transformed B-cell lines (LCL). The effects — if present — were very weak. Short-term interferon (IFN) treatment of the lymphocytes induced cytotoxic potential which could be manifested against autologous and allogeneic LCL. The sensitivity of the targets increased after superinfection with the P3HR-1 strain of EBV. Thus the strongest lytic effects were obtained with IFN-treated lymphocytes acting on EBV superinfected targets. Individuals with and without previous EBV encounter reacted against autologous LCL, indicating that the lysis did not represent an EBV-specific cellular memory. No evidence for alloantigen recognition emerged from the tests.

The role of adherent HLA-DR+ mononuclear cells in autologous and allogeneic MLR.

The aim of this study was to define the significance of HLA-DR+ cells for the in vitro induction of human autoreactive T cell proliferation. Proliferation was induced by autologous or allogeneic non-T cells or EB virus-transformed LCL. Pretreatment of stimulator cells with low concentrations of RAHLA-DR and C and with high amounts of RAHLA-DR alone abolished the capacity to stimulate autologous or allogeneic T cells. This suggested that antigens associated with HLA-DR+ stimulator cells or HLA-DR itself are involved in the induction of this proliferation. At the responder cell level the cytotoxic elimination of HLA-DR+ cells as well as depletion of adherent cells by passage through Sephadex G-10 columns reduced both autoreactive and alloreactive responsiveness. Responses of serologically and physically depleted populations were both restored by reconstitution with mitomycin-C treated autologous adherent cells. These cells were resistant to lysis with T cell specific antibodies and preferentially cooperated with T cells of autologous deprivation. Co-cultivation experiments further revealed that such accessory cells were capable of amplifying T cell proliferation in the presence of suboptimal numbers of autologous LCL. We concluded, therefore, that an HLA-DR+-adherent cell, presumably of monocytic origin, is required for optimal proliferative responsiveness of both autoreactive and alloreactive T cells.