Alloreactive Lymphocytes Research Articles

A novel hypothesis on mechanisms and potential role of host cell membrane proteins incorporated into the viral envelope in alloreactivity

Despite significant advances in transplantation medicine, allograft rejection remains a major challenge in clinical practice. The preexistence of alloreactive lymphocytes is a primary cause of allograft rejection. The forthcoming challenges in clinical transplantation will involve the suppression or eradication of allospecific memory T cells. Viral infections and allograft rejection interact in multiple ways that can compromise the survival of transplanted organs. Evidence is currently accumulating on the incorporation of HLA antigens and other host cell plasma membrane molecules into the viral envelope. A consequence of the viral envelope displaying the HLA signature acquired from the plasma membrane of infected cells is that when virions are transmitted to the next host, the newly infected person became exposed to allogeneic molecules stimulating alloimmunity and generating memory to alloantigens. Thus, successive exposure to viral infections throughout life could potentially contribute to the development of alloimmunity and the generation of numerous clones of memory alloreactive lymphocytes. In this paper a novel hypothesis is developed on the potential role and mechanisms of alloresponse induced by human spread of enveloped viruses. As this hypothesis could aid in the knowledge of preexisting alloreactivity, additional research into the intricacies of virion-incorporated host cell proteins is necessary. A deeper understanding of this dynamic interaction will help promote advances in the long-term acceptance of transplants.

Drug exporter expression correlates with group 3 innate lymphoid cell resistance to immunosuppressive agents

Allogeneic hematopoietic cell transplantation (HCT) is often complicated by graft versus host disease (GvHD), an alloreactive immune response triggered by tissue damage. Interleukin (IL)-22 producing type 3 innate lymphoid cells (ILC3) protect epithelial tissues against chemo(radio)therapy-induced damage, suppress alloreactive T cells and mitigate acute GvHD symptoms after allogeneic HCT. Relatively high numbers of ILC before and after allogeneic HCT has been associated with significantly reduced tissue damage and less acute GvHD. While most transplantation conditioning and GvHD prophylaxis regimens are aimed at eliminating host and alloreactive donor lymphocytes, the effect of these regimens on ILC remain elusive. Here, we studied the effect of conditioning chemotherapy and immunosuppressive agents on the survival, proliferation, activation and function of human ILC3 in vitro. Tonsil-derived ILC3 were activated and incubated with agents commonly used to prevent and treat GvHD. While fludarabine, rapamycin, mycophenolic acid and prednisolone suppressed ILC3 to a similar degree as T cells, the effect of other agents, including cyclosporine A, methotrexate, imatinib, ibrutinib and ruxolitinib, was milder on ILC3 than on T cells. ILC3 are less sensitive to immunosuppressants potentially because of their expression of functionally active ATP Binding Cassette Subfamily B Member 1 (ABCB1) drug exporter proteins. This suggests less intracellular accumulation of immunosuppressive agents, which renders ILC3 resistant to these compounds. The present findings may help to develop strategies to simultaneously maintain the tissue protective properties of ILC3 and at the same time suppress alloreactive lymphocytes, which is important in the prevention and treatment of acute GvHD.

"Off-the-Shelf" Allogeneic CAR Cell Therapy-Neglected HvG Effect.

Chimeric antigen receptor (CAR) cell therapy offers patients with hematological malignancies a new therapeutic option. Traditionally, autologous T cells are used to generate CAR designed T cells for each patient. However, this method has several drawbacks, the development of allogeneic CAR cell therapy would be a promising breakthrough that could address several of these limitations. From the clinical trials that have published data, the efficacy of allogeneic CAR cell therapy did not meet the expectations. Because of the host-versus-graft (HvG) effect, allogeneic CAR cells are eliminated by the host, resulting in short-term persistence of allogeneic CAR cells and poor efficacy. It is critical to solve the HvG effect of allogeneic CAR cells. The current commonly used methods are suppressing the host's immune system, using HLA-matched homozygous donors, reducing the expression of HLA, targeting alloreactive lymphocytes and eliminating anti-CAR activities. In this review, we will focus on the HvG effect of the "off-the-shelf" allogeneic CAR cell therapy, especially its mechanism and current methods to solve this problem and summarize relevant clinical trial data.

Clinical effects of administering leukemia-specific donor T cells to patients with AML/MDS after allogeneic transplant

AbstractRelapse after allogeneic hematopoietic stem cell transplantation (HCT) is the leading cause of death in patients with acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). Infusion of unselected donor lymphocytes (DLIs) enhances the graft-versus-leukemia (GVL) effect. However, because the infused lymphocytes are not selected for leukemia specificity, the GVL effect is often accompanied by life-threatening graft-versus-host disease (GVHD), related to the concurrent transfer of alloreactive lymphocytes. Thus, to minimize GVHD and maximize GVL, we selectively activated and expanded stem cell donor–derived T cells reactive to multiple antigens expressed by AML/MDS cells (PRAME, WT1, Survivin, and NY-ESO-1). Products that demonstrated leukemia antigen specificity were generated from 29 HCT donors. In contrast to DLIs, leukemia-specific T cells (mLSTs) selectively recognized and killed leukemia antigen–pulsed cells, with no activity against recipient's normal cells in vitro. We administered escalating doses of mLSTs (0.5 to 10 × 107 cells per square meter) to 25 trial enrollees, 17 with high risk of relapse and 8 with relapsed disease. Infusions were well tolerated with no grade >2 acute or extensive chronic GVHD seen. We observed antileukemia effects in vivo that translated into not-yet-reached median leukemia-free and overall survival at 1.9 years of follow-up and objective responses in the active disease cohort (1 complete response and 1 partial response). In summary, mLSTs are safe and promising for the prevention and treatment of AML/MDS after HCT. This trial is registered at www.clinicaltrials.com as #NCT02494167.

Engineered off-the-shelf therapeutic T cells resist host immune rejection.

Engineered T cells are effective therapies against a range of malignancies, but current approaches rely on autologous T cells, which are difficult and expensive to manufacture. Efforts to develop potent allogeneic T cells that are not rejected by the recipient's immune system require abrogating both T- and natural killer (NK)-cell responses, which eliminate foreign cells through various mechanisms. In the present study, we engineered a receptor that mediates deletion of activated host T and NK cells, preventing rejection of allogeneic T cells. Our alloimmune defense receptor (ADR) selectively recognizes 4-1BB, a cell surface receptor temporarily upregulated by activated lymphocytes. ADR-expressing T cells resist cellular rejection by targeting alloreactive lymphocytes in vitro and in vivo, while sparing resting lymphocytes. Cells co-expressing chimeric antigen receptors and ADRs persisted in mice and produced sustained tumor eradication in two mouse models of allogeneic T-cell therapy of hematopoietic and solid cancers. This approach enables generation of rejection-resistant, 'off-the-shelf', allogeneic T-cell products to produce long-term therapeutic benefit in immunocompetent recipients.

Photodepletion with 2-Se-Cl prevents lethal graft-versus-host disease while preserving antitumor immunity.

Acute graft-versus-host-disease (GVHD), limits the use of hematopoietic cell transplant (HCT) to treat a variety of malignancies. Any new therapeutic approach must satisfy three requirements: 1) Prevent GVHD, 2) Maintain anti-pathogen immunity, and 3) Maintain anti-tumor immunity. In prior studies we have shown that the selective photosensitizer 2-Se-Cl eliminates highly alloreactive lymphocytes from the graft prior to HCT preventing GVHD and that antiviral immune responses were preserved following incubation with 2-Se-Cl. In this report, we investigated whether 2-Se-Cl treatment preserves antitumor immunity, and then used high dimensional flow cytometry to identify the determinants of successful immune reconstitution. Donor C57BL/6 splenocytes were cocultured for 4 days with irradiated BALB/c splenocytes and then exposed to 2-Se-Cl. Photodepletion (PD)-treated splenocytes were then infused into lethally irradiated BALB/c mice inoculated with A20 leukemia/lymphoma cells. Recipient mice that received PD-treated splenocytes survived > 100 days without evidence of GVHD or leukemia. In contrast, mice that did not receive PD-treated cells at time of HCT died of leukemia progression. Multiparameter flow cytometry of cytokines and surface markers on peripheral blood samples 15 days after HCT demonstrated unique patterns of immune reconstitution. We found that before clinical disease onset GVHD was marked by functionally exhausted T cells, while tumor clearance and long-term survival were associated with an expansion of polyfunctional T cells, monocytes, and DCs early after transplantation. Taken together these results demonstrate that 2-Se-Cl photodepletion is a new treatment that can facilitate HCT by preventing GVHD while preserving antiviral and anti-tumor immunity.

Targeting non-engrafting IL-2 activated intentionally mismatched donor lymphocytes with monoclonal or bispecific antibodies for treatment of otherwise incurable cancer.

e15033 Background: Cure of certain resistant cancers by donor lymphocyte infusion (DLI) following allogeneic stem cell transplantation (SCT) suggests that alloreactive lymphocytes can eliminate otherwise resistant cancer. First patient with resistant relapse following supra-lethal chemoradiotherapy treated with DLI is alive & well > 34 years; > 400 patients with hematological malignancies confirmed DLI efficacy for prevention & treatment of relapse. Using murine leukemia (BCL1) & metastatic breast cancer (4T1), IL-2 activated mismatched lymphocytes with no prior SCT eliminated otherwise lethal minimal residual disease (MRD). Using anti-EpCAM x anti-CD3 bispecific antibody (BSA) lethal melanoma was eliminated, also resulted in long-lasting immunity against lethal tumor challenge. Graft-vs-host disease (GVHD) was prevented by consistent rejection of mismatched lymphocytes. Accordingly, our goal was to develop effective immunotherapy of cancer using non-engrafting intentionally mismatched Allogeneic Targeted Activated Cancer Killer cells (ATACK) using relevant monoclonal antibodies (MoAb) or BSA. Methods: Patients with multiple myeloma & lymphoma and advanced solid tumors were treated with haploidentical or unrelated donor lymphocytes pre-activated 5 days with IL-2, following non-myeloablative conditioning with endoxan or fludarabine and IL-2 injection x5 days for in vivo lymphocyte activation. ATACK with no MoAb was investigated in 40 patients with different cancers. Safety of ATACK with MoAb was investigated in 16 patients with resistant NHL, metastatic breast, lung & colorectal cancer, using commercial MoAbs against CD20, Her-2, EGFR or VEGF, respectively, or using anti-EpCAM BSA. Results: Protocols were well-tolerated with mild transient toxicity following ATACK and BSA. No patient developed GVHD. Disease-free survival > 15 years was documented in 2/2 patient with multiple myeloma and 2/2 patients with lymphoma. Longterm progression-free survival was observed in 5/31 evaluable patients with advanced metastatic solid tumors treated with no MoAbs. Minor toxicity in targeted ATACK recipients was manageable in outpatient clinic. Conclusions: Intentionally mismatched IL-2 activated killer cells guided by MoAbs or BSA represents a promissing approach for treatment, possibly even cure, of cancer patients with MRD while avoiding GVHD.

A mathematical model for dynamics of soluble form of DNAM-1 as a biomarker for graft-versus-host disease.

DNAM-1 (CD226) is an activating immunoreceptor expressed on T cells and NK cells and involved in the pathogenesis of acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We previously reported that a soluble form of DNAM-1 (sDNAM-1) is generated by shedding from activated T cells. Moreover, higher serum levels of sDNAM-1 in patients before allo-HSCT is a predictive biomarker for the development of aGVHD based on the retrospective univariate and multivariate analyses in allo-HSCT patients. However, it remains unclear how the serum levels of sDNAM-1 are regulated after allo-HSCT and whether they are associated with the development of aGVHD. Here, we constructed a mathematical model to assess the dynamics of sDNAM-1 after allo-HSCT by assuming that there are three types of sDNAM-1 (the first and the second were from alloreactive and non-alloreactive donor lymphocytes, respectively, and the third from recipient lymphocytes). Our mathematical model fitted well to the data set of sDNAM-1 in patients (n = 67) who had undergone allo-HSCT and suggest that the high proportion of the first type of sDNAM-1 to the total of the first and second types is associated with high risk of the development of severe aGVHD. Thus, sDNAM-1 after allo-HSCT can be a biomarker for the development of aGVHD.

Role of MMP-13 in Graft-Versus-Host Disease

Matrix metalloproteinases (MMPs) have been initially recognized for their role in degradation of extracellular matrix (ECM) and collagen remodeling. However, MMPs have been shown to play a crucial role in inflammation, tumor cell invasion, adaptive and innate immunity. Acute and chronic Graft versus Host Disease (GVHD) are characterized by distinctive histopathological features involving tissue infiltration with donor cells, tissue damage and remodeling. We therefore hypothesized that GVHD-associated organ damage may involve MMPs. We have now identified a novel immunomodulatory function for MMP-13 (alternatively called collagenase-3)and have uncovered a previously unknown role of MMP-13 in regulating GVHD.To address the function of MMP-13 in GVHD we first assesed the effect of MMP-13 on alloresponses in vitro. Using fully Major Histocompatibility Complex (MHC)-mismatched standard mixed lymphocyte reaction we demonstated that antigen presentig cells (APC) from B6.MMP-13-/-(H2b) mice led to signifcantly enhanced antigen-driven activation and proliferation of Carboxyfluorescein succinimidyl ester (CFSE)-labeled Balb/c responder splenocytes. Thus, MMP-13 deficiency in either splenocytes or bone marrow-derived dendritic cells used as stimulators resulted in enhanced proliferation, activation and IFN-gproduction in the allo-reactive lymphocyte responders. Similarly, exogenous MMP13 reduced proliferation of responder T cells as determined tested by CFSEdilution (CFSEloof CD4+T cells from 62.3% decreased to 40.6%, CFSEloof CD8+T cells from 74.1% down to 47.9%). We next assessed the impact of MMP-13 in vivousing fully MHC-mismatched rodent acute GVHD models. To study the role of host-derived MMP-13 we induced GVHD in B6.MMP-13-/-or B6.WT recipient mice following lethal TBI (1075 rad) using splenic T cells from Balb/cdonors. We observed signifcantly accelerated GVHD-related mortality (Median Survival Time 7 vs. 47 days post-transplant, p<0.05) in MMP-13-deficient recipients. Most importantly, donor T cells expanded more vigorously in the secondary lymphoid organs (Spleen and mesenteric lymphnoodes) of MMP13-/-compared to wildtype recipient mice (e.g. spleen: absolute donor CD4+Tcells 1.5x104± 7.3 x 103 (WT) vs. 5.83 x104±1.65 x104[MMP-13-/-] and CD8+5.5 x104± 3.8 x104(WT) vs 3.4 x105±1.4 x105[MMP-13-/-], p<0.01). Enhanced donor lymphocyte expansion was further confirmed by bioluminescence imaging. To further delineate the underlying mechanisms, we analyzed the effects of MMP-13deficiency and exogenous MMP-13 on maturation of mouse bone marrow derived-dendritic cells (BMDC) and macrophages in vitro. We noted decreased expression of inhibitory molecules PD-L1 and PD-1H on GM-CSF/LPS cultured BMDC. Similarly, bone marrow-derived MMP-13-/-macrophages also showed reduced PD-L1 and PD-1H expression upon LPS stimulation when compared to their WT counterparts. In summary we posit that recipient myeloid cell-derived MMP-13 mitigates GVHD and limits donor T cell expansion. Further studies are warranted to determine how MMP-13 suppresses expansion of donor T cells and impacts Graft-versus-Leukemia responses. Disclosures Lentzsch: Caelum Biosciences: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Bayer: Consultancy; Janssen: Consultancy; Takeda: Consultancy; Abbvie: Consultancy; Clinical Care Options: Speakers Bureau; Sanofi: Consultancy, Research Funding; Multiple Myeloma Research Foundation: Honoraria; International Myeloma Foundation: Honoraria; Karyopharm: Research Funding; Columbia University: Patents & Royalties: 11-1F4mAb as anti-amyloid strategy; Proclara: Consultancy; BMS: Consultancy.

Exploiting autoimmunity unleashed by low-dose immune checkpoint blockade to treat advanced cancer.

As a result of the cancer immunotherapy revolution, more than 2000 immuno-oncology agents are currently being tested or are in use to improve responses. Not unexpectedly, the 2018 Nobel Prize in Physiology or Medicine was awarded to James P. Allison and Tasuku Honjo for their development of cancer therapy by the blockade of co-inhibitory signals. Unfortunately, manipulation of the co-inhibitory receptors has also resulted in a safety issue: widespread iatrogenic immune-related adverse events (irAEs). Autoimmunity is emerging as the nemesis of immunotherapy. Originally, it was assumed that CTLA-4 blockade selectively targets T cells relevant to the antitumour immune response. However, an uncontrolled pan T cell activation was induced compromising tolerance to healthy self-tissues. The irAEs are very similar to that of a chronic graft-versus-host-disease (GVHD) reaction following allogeneic bone marrow transplantation (BMT). We hypothesized that ipilimumab induced a graft-versus-malignancy (GVM) effect, which eradicated metastatic melanoma in a minority of patients, but also involved an auto-GVHD reaction that resulted in widespread autoimmunity in the majority. Therefore, we argued for a profound theoretical point against the consensus of experts. The task is not to desperately put the genie back in the bottle by immune-suppressive treatments, but instead to harness the autoimmune forces. In this way, the same goal could be achieved by an antibody as by the adoptive transfer of alloreactive donor lymphocytes, but without severe GVHD. The proof-of-principle of a low-dose-combination immune checkpoint therapy, consisting only of approved drugs and treatments, was demonstrated in 111 stage IV cancer patients.

Potential of Membranes Surrounding the Fetus as Immunoprotective Cell-Carriers for Allogeneic Transplantations.

Membranes surrounding the fetus play a crucial role in providing a physical and immunological barrier between a semiallogeneic fetus and mother during pregnancy. In this study, we tested whether cotransplantation of fetal membranes (FMs) and allogeneic donor cells would improve the retention and function of allografts in mice. Intact and enzyme-digested membranes obtained from E18-E19 pregnant mice were subcutaneously cotransplanted with 10F7MN hybridoma cells that are of BALB/cByJ (Balb) origin and secrete anti-human CD235a antibody. Cells were transplanted into C57BL/6J (B6, allogeneic), Balb (syngeneic), and FVB/NJ (third-party) mice. Serum was collected after 1 and 3 weeks of cell transplantation and tested using flow cytometry for the presence of anti-human CD235a antibody. Immunosuppressive functions of membranes were further investigated by analyzing the cytokine profile of supernatants collected from allo-reactive mixed lymphocyte reactions (MLRs) using a multiplex cytokine assay. B6 mice transplanted with 10F7MN cells along with membranes syngeneic to the host had significantly higher levels of CD235a antibody when compared to B6 mice that received cells without membranes, allogenic membranes, or third-party membranes. Syngeneic membranes significantly inhibited T-cell proliferation in the presence of allogeneic stimuli and suppressed the release of Th1-cytokines such as IFNγ, TNFα, and IL-2 in MLRs. Additionally, increases in the levels of Th2-cytokines were found in MLRs containing membrane-derived cells. Our study highlights the potential use of syngeneic FMs to act as potent cell-carriers that could improve graft retention as well as graft-specific immunoprotection during allograft transplantation.

Potential elimination of multi-drug resistant cancer cells by targeted non-engrafting intentionally mismatched activated donor lymphocytes.

e14007 Background: Immunotherapy by targeted autologous T cells, TIL or CAR-T, are considered most effective modalities for treatment of otherwise resistant cancer, yet cure is rarely achieved. In contrast, cure of resistant disease by donor lymphocyte infusion (DLI) following allogeneic stem cell transplantation suggests that alloreactive lymphocytes represent a most effective approach for elimination of resistant malignant cells. The first patient relapsing following supra-lethal chemoradiotherapy is alive & well > 34 years. Using murine B cell leukemia (BCL1) and metastatic breast cancer (4T1) we proved that non-engrafting intentionally mismatched lymphocytes activated with IL-2 that were consistently rejected cured otherwise lethal cancer with no graft-vs-host disease (GVHD). Methods: We first applied graft-vs-tumor effects by non-engrafting Intentionally Mismatched Activated Killers (IMAK) following mild immunosuppressive conditioning to maximize homeostatic proliferation of activated T & NK cells. IMAK was first applied inpatients with multiple myeloma and lymphoma treated with donor lymphocytes pre-activated in vitro prior to infusion and for 5 days following infusion withlow dose IL-2.We next studied feasibility of Allogeneic Targeted Activated Cancer Killer cells (ATACK) using IL-2 activated haploidentical donor lymphocytes including T & NK cells targeted against antigens over-expressed on the surface of malignant cells: Her-2/neu, EGFR, VEGF and CD20 using commercially available Herceptin, Erbitux, Avastin or Rituximab, respectivelyin a pilot study involving 16 patients with advanced metastatic solid tumors. Results: Using IMAK donor lymphocytes were uniformly rejected and no patient developed GVHD. Disease-free survival > 20 years was documented in our first myeloma patient with plasmacytomas and in another relapsing after autologous SCTand in 2 patients with non-Hodgkin lymphoma. Longterm progression-free survival was reported in 5 of 31 patients with resistant solid tumors. Following ATACK transient mild toxicity was manageable in outpatient clinic and no GVHD developed. Conclusions: Using ATACK against minimal residual disease accomplishable by most cancer patients following conventional 1st line treatment may result in cure of otherwise resistant cancer while avoiding GVHD.

HLA-DQ alloantibodies directly activate the endothelium and compromise differentiation of FoxP3high regulatory T lymphocytes

Development of donor-specific antibodies is associated with reduced allograft survival in renal transplantation. Recent clinical studies highlight the prevalence of human leukocyte antigen (HLA)-DQ antibodies amongst de novo donor-specific antibodies (DSAs), yet the specific contribution of these DSAs to rejection has not been examined. Antibody-mediated rejection primarily targets the microvasculature, so this study explored how patient HLA-DQ alloantibodies can modulate endothelial activation and so immunoregulation. HLA-DQ antibodies phosphorylated Akt and S6 kinase in microvascular endothelial cells. This activation prior to culture with alloreactive lymphocytes increased IL-6 and RANTES secretion. The antibody-mediated upregulation of IL-6 was indeed Akt-dependent. The binding of HLA-DQ antibodies to endothelial cells selectively reduced T cell alloproliferation and FoxP3high Treg differentiation. In clinical studies, detection of HLA-DQ DSAs with other DSAs is associated with worse graft survival than either alone. Endothelial cells stimulated with HLA-DR and HLA-DQ antibodies showed a synergistic increase in pro-inflammatory cytokine secretion and a decrease in Treg expansion. HLA-DQ antibodies strongly promote pro-inflammatory responses in isolation and in combination with other HLA antibodies. Thus, our data give new insights into the pathogenicity of HLA-DQ DSAs.

Rejection-resistant off-the-shelf T cells for adoptive cell therapy

Abstract ‘Off-the-shelf’ (OTS) chimeric antigen receptor (CAR) T cells pre-manufactured from healthy donors are a readily available and less expensive alternative to autologous products. However, immune rejection of OTS cells by host T- and NK-cells may limit their persistence and reduce therapeutic effect. Here, we engineered rejection-resistant OTS T cells that recognize and eliminate alloreactive lymphocytes while retaining desired anti-tumor activity. As T- and NK-cells transiently upregulate 4-1BB after activation, T cells expressing a 4-1BB-specific alloimmune defense receptor (ADR) selectively eliminated activated T- and NK-cells while sparing resting lymphocytes. Using this mechanism, ADR-expressing T cells suppressed alloimmune activation and resisted rejection in a mixed lymphocyte reaction (MLR) model in vitro. Further, T cells co-expressing the ADR and a CD19 CAR retained undiminished activity through both receptors in vitro and in vivo. We established a mouse model of allogeneic cell therapy in which NSG mice were engrafted with systemic CD19+ leukemia and normal human T cells. In this model, adoptively transferred unmodified CD19 CAR T cells from an HLA mismatched donor produced only transient anti-tumor activity and were rapidly rejected by pre-engrafted alloreactive T cells within 7 days, leading to fatal leukemia relapse. In contrast, T cells co-expressing both CAR and ADR were protected from immune rejection, resulting in long-term persistence (>9 weeks) and durable leukemia eradication in most animals. These data support the feasibility of using ADR to generate highly potent OTS CAR T cell products that suppress immune rejection to produce long-term therapeutic benefit even in immunocompetent patients.

Rejection-Resistant Off-the-Shelf T Cells for Adoptive Cell Therapy

Introduction Autologous therapeutic T cells can cure life-threatening diseases but their manufacturing remains expensive and time-consuming. ‘Off-the-shelf' (OTS) T cell products pre-manufactured from healthy donors are potentially a readily available and less expensive alternative, offering similar therapeutic potency. However, immune rejection by host T- and NK-cells may limit the persistence of OTS cells and compromise their anti-tumor activity. Objectives To enhance the persistence of OTS T cells by engineering resistance to alloimmune rejection. Methods We engineered Alloimmune Defense Receptors (ADRs) that enable OTS T cells to recognize and eliminate alloreactive lymphocytes. We demonstrated ADR-expressing virus-specific (VST) and chimeric antigen receptor (CAR)-expressing T cells resist immune rejection in several in vitro and in vivo models. Results Expression on T cells of ADR specific to 4-1BB and OX40 – costimulatory molecules transiently upregulated on activated T- and NK-cells – enabled specific elimination of activated T cells. Consistent with the expression pattern of ADR targets, 4-1BB ADR T cells preferentially targeted activated CD8+ T cells while OX40 ADR T cells were more selective against CD4+ T cells. Neither ADR produced any discernable activity against resting lymphocytes in peripheral blood. In an in vivo model of allogeneic T-cell rejection, where NSG mice were engrafted with systemic CD19+ leukemia and normal activated PBMC, allogeneic CD19 CAR T cells were rapidly rejected by alloreactive lymphocytes and failed to control systemic leukemia long-term. In contrast, CD19 CAR T cells co-expressing the 4-1BB ADR were fully protected from immune rejection, persisted long term in vivo, and eradicated the tumor (Fig.1). Further, 4-1BB- or OX40- ADR expressing VSTs, which themselves lack alloreactivity when used clinically, were protected from immune rejection by alloreactive T- and NK- cells in an in vitro mixed lymphocyte reaction model, and retained undiminished anti-viral activity. Conclusion These data demonstrate the efficacy of ADRs as first-in-class engineered receptors suppressing immune rejection of OTS VST and CAR-T cell therapies.

Cardiosphere-derived cells suppress allogeneic lymphocytes by production of PGE2 acting via the EP4 receptor

Cardiosphere-derived cells (CDCs) are a cardiac progenitor cell population, which have been shown to possess cardiac regenerative properties and can improve heart function in a variety of cardiac diseases. Studies in large animal models have predominantly focussed on using autologous cells for safety, however allogeneic cell banks would allow for a practical, cost-effective and efficient use in a clinical setting. The aim of this work was to determine the immunomodulatory status of these cells using CDCs and lymphocytes from 5 dogs. CDCs expressed MHC I but not MHC II molecules and in mixed lymphocyte reactions demonstrated a lack of lymphocyte proliferation in response to MHC-mismatched CDCs. Furthermore, MHC-mismatched CDCs suppressed lymphocyte proliferation and activation in response to Concanavalin A. Transwell experiments demonstrated that this was predominantly due to direct cell-cell contact in addition to soluble mediators whereby CDCs produced high levels of PGE2 under inflammatory conditions. This led to down-regulation of CD25 expression on lymphocytes via the EP4 receptor. Blocking prostaglandin synthesis restored both, proliferation and activation (measured via CD25 expression) of stimulated lymphocytes. We demonstrated for the first time in a large animal model that CDCs inhibit proliferation in allo-reactive lymphocytes and have potent immunosuppressive activity mediated via PGE2.

Cell-Based Therapies in Vascularized Composite Allotransplantation.

Dendritic cells (DCs) are bone marrow-derived, professional antigen-presenting cells with tolerogenic function. The ability of DCs to regulate alloantigen-specific T cell responses and to promote tolerance has aligned them ideally for a role in vascularized composite allotransplantation (VCA). In this study, we summarize the current evidence for DC therapies for tolerance induction to alleviate the requirement for chronic immunosuppression. A comprehensive and structured review of manuscripts published on VCA was performed using the MEDLINE and PubMed databases. All eligible studies published from the year 2000 to 2017 were included in the final results. Nineteen original preclinical and clinical studies that employed cell therapy for VCA were included in this review. In vivo DC therapy was found to direct the alloimmune response toward either transplant rejection or tolerance in VCA models. While injection of mature DCs rapidly increases T-cell activity in humans and promotes transplant rejection, the injection of immature DCs acts as an immunosuppressant and inhibits T-cell activity. In addition to immature DCs, mesenchymal stem cells were also found to have a positive effect on allotransplantation of solid organs and bone marrow via cytokine expression which decreases the alloreactive effector lymphocytes and increases CD4+/CD25+/FoxP3 Tregs. Despite the promising findings, the efficacy of cell-based therapies varies greatly across studies, partly due to different methods of cell isolation and purification techniques, source, route and timing of administration, and combination immunosuppressive therapy. Additional research is needed to evaluate the efficacy and safety of DC and other cell-based therapeutic measures in human allotransplant recipients. Future direction will focus on the development of novel methods to reduce immunosuppression and develop more individualized management, as well as the clinical application of basic research in the mechanisms of immunologic tolerance.

Bilirubin Nanoparticle as an anti-inflammatory therapy for graft versus host disease

Abstract Graft versus host disease (GvHD) caused by alloreactive donor lymphocytes is a fatal complication of hematopoietic stem cell transplant (HSCT). Conditioning regimen consisting of chemotherapy and/or radiation given prior to HSCT can cause the initial tissue damage, which triggers the cross-presentation of alloantigens to the donor immune cells. Previous studies have shown that water-soluble PEGylated bilirubin nanoparticles (BRNP) selectively accumulate at the site of inflammation and prevent further tissue damage through scavenging reactive oxygen species. Therefore we, hypothesized that BRNP treatment after conditioning regimen can reduce GvHD by abating the initial tissue damage in HSCT, and investigated therapeutic efficacy of BRNP using murine GVHD model. Sublethally irradiated recipient mice (Balb/c) were infused with 4×106 bone marrow and 1×106 splenic T cells from donor mice (C57/B6) on day 1, and with or without BRNP (10mg/kg) on days 0, 2, and 4. GvHD symptoms were monitored for 60 days, and scored for changes in fur, skin, posture, activity, and weight. Untreated recipient mice (n=9) developed significantly worse GVHD (mean GVHD score=4.667) compared to BRNP treated recipient mice (n=9, mean GVHD score=1.556) (p=0.0028). This translated into the significantly better survival of BRNP treated mice with day 60 survival of 65% as compared to the untreated recipient mice with day 60 survival of 11% (p=0.03). In summary, we show that BRNP treatment can ameliorate clinical GvHD symptoms and improve survival in murine GVHD model. In the future, we plan to investigate the role of reactive oxygen species in GVHD and mechanism of action on anti-GVHD effects by BRNP.

Peripheral Blood Grafts for T Cell–Replete Haploidentical Transplantation Increase the Incidence and Severity of Cytokine Release Syndrome

T cell–replete post-transplant cyclophosphamide (PTCy)-based protocols have led to increasing use of haploidentical allogeneic hematopoietic cell transplantation (haploHCT). With this approach, bidirectional alloreactivity causing nonengraftment or severe graft-versus-host disease (GVHD) is no a longer major barrier to haploHCT. PTCy eliminates alloreactive lymphocytes but spares CD34+ stem cells and regulatory T lymphocytes, resulting in reliable hematopoietic recovery with relatively low incidence of GVHD. The immediate post-haploHCT course, usually before PTCy administration, is often complicated by cytokine release syndrome (CRS). The predictors of CRS and its effect on outcomes post-transplant have not been fully ascertained. We analyzed the outcomes of 66 patients who received haploHCT at our institution. Using published CRS criteria we identified 48 patients who developed CRS. In multivariate analysis peripheral blood grafts were significantly associated with grade ≥ 2 CRS, compared with bone marrow. Grade ≥ 2 CRS (compared with grade < 2) was not associated with differences in overall survival or nonrelapse mortality. Severe CRS was associated with a statistically nonsignificant trend toward higher incidences of grades III to IV acute GVHD, especially in the context of peripheral blood grafts. CRS is a common complication after T cell–replete peripheral blood haploHCT, but post-transplant survival outcomes may not be affected in those with severe CRS.

The Role of the Endothelium during Antibody-Mediated Rejection: From Victim to Accomplice.

Antibody-mediated rejection (AMR) of solid organ transplants is characterized by the activation and injury of the allograft endothelium. Histological and transcriptomic studies have associated microvascular inflammation and endothelial lesions with the severity of rejection and poor graft outcomes. The allograft endothelium forms the physical barrier between the donor organ and the recipient; this position directly exposes the endothelium to alloimmune responses. However, endothelial cells are not just victims and can actively participate in the pathogenesis of rejection. In healthy tissues, the endothelium plays a major role in vascular and immune homeostasis. Organ transplantation, however, subjects the endothelium to an environment of inflammation, alloreactive lymphocytes, donor-specific antibodies, and potentially complement activation. As a result, endothelial cells become activated and have modified interactions with the cellular effectors of allograft damage: lymphocytes, natural killer, and myeloid cells. Activated endothelial cells participate in leukocyte adhesion and recruitment, lymphocyte activation and differentiation, as well as the secretion of cytokines and chemokines. Ultimately, highly activated endothelial cells promote pro-inflammatory alloresponses and become accomplices to AMR.