Post-transplant Viral Infections Research Articles

Intravenous Immunoglobulin in BK Virus Nephropathy

The incidence of post transplant viral infections has increased with the use of more potent immunosuppressive regimens. Consequently, BK virus nephropathy (BKVN) has arisen as a significant cause of graft dysfunction and loss. Reduction of immunosuppression is the first line management of post-transplant viral infections. Other therapies such as intravenous immunoglobulin (IVIg), cidofovir, leflunomide and fluoroquinolones have been tried with varying degrees of success.

Subclinical Epstein - Barr Virus Viremia Is Associated With Decline GFR in Kidney Transplantation: Single Center Experience.

Purpose: Post-transplant viral infection is a known risk factor for graft dysfunction and malignancies including PTLD. However, the impact of subclinical Epstein-Barr virus (EBV) infection on allograft injury in the renal transplant population has not yet been well defined. Method: A single center study was conducted from Oct, 2012 to Apr, 2013.We assessed EBV viremia by PCR in 327 renal transplant recipients. Results: Subclinical EBV viremia occurred in 14.7%. A multivariable linear regression analysis suggested that subclinical EBV infections are significantly associated with declines in GFR (-2.34 ± 7.00 ml/min vs. 0.98 ± 8.17 ml/min, p<0.05), log proteinuria and duration since transplantation. Conclusion: Our data demonstrated that there is an association between subclinical EBV infections and adverse outcomes in renal transplant patients, despite appropriate post-transplant antiviral prophylaxis. These findings support the need for serial viral monitoring for better outcomes in renal transplant patients.

Blood Dendritic Cell Levels Associated With Impaired IL-12 Production and T Cell Function in Kidney Disease: Implications for Post-Transplant Viral Infections.

Background: We previously demonstrated a reduction of blood myeloid dendritic cell (mDC) levels in patients with kidney disease pre-transplant that is associated statistically with the development of BK viremia and CMV disease post-transplant. However, the mechanisms by which mDC levels might influence these outcomes have not been elucidated. In the current report, we studied the association of mDC levels with mDC IL-12 production and T cell level/function. Methods: Peripheral blood was studied in 3 groups: (i) patients with end stage renal disease at hemodialysis units (HD; n=81); (ii) patients with kidney disease presenting for kidney transplant evaluation or transplantation (Eval/Tx; n=323); and (iii) healthy controls (HC; n=22). Peripheral blood mononuclear cell levels were measured by flow cytometry. IL-12 production was assessed by intracellular staining and multiplex assay. T cell IFN-g responses were measured by ELISpot assay. Results: Along with significant reduction in mDC levels, significantly reduced CD8+ T cell and monocyte levels were also demonstrated in the kidney disease groups compared to HC. Furthermore, levels of CD8+ T cells, which are stimulated by DCs and important to antiviral immunity, correlated positively with the deficient DC levels observed in kidney disease patients. Significantly reduced peripheral blood mDC and monocyte-derived DC (MoDC) IL-12 production was observed after in vitro LPS stimulation in the HD vs HC groups. Finally, addition of autologous MoDCs with or without CMV peptide to T cell culture failed to increase significantly the number of IFN-g responses in the HD group in contrast to that observed for the HC group. Conclusions: Peripheral blood mDC level deficiency in patients with kidney disease is associated with deficient IL-12 production and T cell level/function, which may explain the known correlation of CD8+ T cell lymphopenia with deficient antiviral responses following kidney transplantation.

Improvement in Quality of Care Metrics Through The Implementation of Electronic Health Records (EHR) in Renal Transplant Patient Management.

Objective: Present our experience with Electronic Health Records (EHR) in Clinical Decision Support (CDS), Computerized Physician Order Entry (CPOE), and Health Information Exchange (HIE) in renal transplant care. Methods: Apply EHR for standardized post transplant care A)Implement protocols and flow sheets 1) Establish unified template note and flow sheets (TX chemistry, TX anemia, Tx CVD risk, Tx virology, TX HLA) 2) Establish clinical pathways with CDS to detect allograft dysfunction, drug levels, DSA's, viral surveillance and protocol biopsies. 3) Manage CDC high risk organs recipients with viral monitoring. 4) Manage post-transplant viral infections (CMV, BKV) to reduce treatment variability and improve outcomes. B) Communication: Implement HIE to improve communication between patients and staff, immediate availability of lab results and medication refills through E-prescribing. Lab results download into patient charts with critical alerts. Patients received results via secure health track emails. C) Patient care: Improved monitoring for compliance with lab testing, medication refills and follow up. Periodic reports for “at risk patients” allowed focused interventions. D) Established a standardized note to reduce variability, decrease error, and improved the quality of care. Results: At our center we performed 192 kidney alone transplants in 2013 and achieved 100% compliance with chemistry testing monitoring, 90% BKV screening, and 78% protocol biopsy. We have unified patient care for BKV infection and acute allograft rejection. We noticed an improvement in 1-year actual allograft survival (Figure) with 6m allograft survival of 98% (transplanted in 2013). Conclusion: Adopting a unified approach to patient care using EHR resulted in improvement in quality metrics via protocols and flow sheets, monitoring of compliance and better communications. The use of EHR has been associated with effective patient care with a trend towards better outcome.Figure: No Caption available.

Naïve T-cell-derived CTL recognize atypical epitopes of CMVpp65 with higher avidity than CMV-seropositive donor-derived CTL - a basis for treatment of post-transplant viral infection by adoptive transfer of T-Cells from virus-naïve donors

Naïve T-cell-derived CTL recognize atypical epitopes of CMVpp65 with higher avidity than CMV-seropositive donor-derived CTL - a basis for treatment of post-transplant viral infection by adoptive transfer of T-Cells from virus-naïve donors

Blood Dendritic Cell Deficiency Associated with Impaired IL-12 Production and T Cell Deficiency in Patients with End Stage Renal Disease: Implications for Post-Transplant Viral Infections

Blood Dendritic Cell Deficiency Associated with Impaired IL-12 Production and T Cell Deficiency in Patients with End Stage Renal Disease: Implications for Post-Transplant Viral Infections

IL-2 withdrawal from human CD8+ T cell expansion in the presence of IL-7 enables retention of favorable functional and phenotypic characteristics for adoptive immunotherapy (165.2)

Abstract Viral infection and reactivation of latent viruses are major causes of mortality and morbidity following haematopoietic stem cell transplantation. Adoptive immunotherapy with CD8+ T cells has proven efficacy in preventing or treating post-transplant viral infection, including therapy with resting T cells that undergo homeostatic expansion in vivo that follows transplantation. However T cells continuously expanded in vitro in IL-2 lose many characteristics associated with efficacy in vivo, and most IL-2-expanded cells die soon after infusion. Here we describe an alternative expansion protocol for human CD8+ T cells that only exposes the cells briefly to IL-2. Survival of the cells after IL-2 withdrawal relies on the continuous presence of IL-7, and the cells eventually come to rest in the cultures. In this system, timed exposure of naïve CD8+ T cells to IL-12 and IL-21 generates memory cells with competent effector functions upon rechallenge, specifically strong production of IFNγ, TNFα and IL-2. The memory cells generated also have acquired a favourable phenotype associated with early differentiation status by both cell surface markers (CCR7, CD62L, CD27 and CD28) and transcription factors (eg Tcf-1). Although our system has been piloted on the expansion of naïve CD8+ T cells, we propose that this alternative protocol could be used to generate resting antigen-specific memory cells with improved efficacy in preventing or treating viral disease in immunocompromised patients.

Moving Successful Virus-specific T-cell Therapy for Hematopoietic Stem Cell Recipients to Late Phase Clinical Trials

There are now multiple effective strategies for the activation and expansion, or direct selection of virus-specific T cells that may be able to eliminate a range of virus infections in the immunocompromised host. In this mini-review, we explain how the stage is set for their rigorous evaluation in large-scale clinical trials. Virus infections are the cause of 30% or more of transplant-related deaths in recipients of T-cells depleted, allogeneic hematopoietic stem cell transplants (HSCT).1 Epstein-Barr virus (EBV), cytomegalovirus (CMV), and adenoviruses (AdV) are the most common culprits, but other common viruses like parainfluenza virus, respiratory syncytial virus, influenza viruses, polyomaviruses, and human herpesvirus 6 together contribute significant morbidity and mortality (Figure 1).2,3,4 Small molecule therapies are often ineffectual, always costly and frequently produce significant adverse effects. Figure 1 Relative frequency of viral infections after HSCT. Adv, adenovirus; BK, JC, KI, and WU (polyomaviruses); CMV, cytomegalovirus; H1N1, influenza strain Hemagglutinnin 1 Neuraminidase 1); HHV, human herpes virus; HSCT, hematopoietic stem cell transplant; ... Virus-specific T-cells derived from stem cell donors can prevent and treat post-transplant viral infections, in the recipients for whom they were intended, and also in partially human leukocyte antigen (HLA)-matched, third party recipients.5,6,7 The low toxicity and long-term protection provided by virus-specific T-cells compares favorably with the significant toxicities and short-term effects of most antivirals.5,6,8,9,10 Is it time, therefore, to begin the transfer of T-cell manufacturing from academic phase I/II clinical trials into hospital or industry-supported facilities so that virus-specific T-cells can be made available to all high-risk HSCT recipients? Several barriers prevent the broader use of virus-specific T-cell therapies after stem cell transplantation. While T-cell therapies for EBV, CMV, and AdV have clearly demonstrated their safety and efficacy both as prophylaxis and as therapy, for many other viruses, the antigens that induce protective T-cells have yet to be identified. Moreover, these infections may occur in <5% of patients making it difficult to perform the rigorous comparative effectiveness studies that will be required to show lower overall cost, fewer adverse effects, and equivalent or superior efficacy. Before any of these barriers can be breached effectively by the academic institutions who are the major developers of these T-cells therapeutics, we must select and optimize manufacturing strategies that are robust and scalable and have the lowest possible cost. Finally, the leap to late phase trials cannot be accomplished by academic institutions alone, but requires partnership with industry. This article will largely deal with selection and optimization of virus-specific T-cell manufacturing strategies.

The prevalence of the most important viral infections in renal transplant recipients in Serbia

Viruses are the main cause of opportunistic infections after kidney transplantation. The aim of this study was to determine the prevalence of cytomegalovirus (CMV), Epstein-Barr virus (EBV), B. K. virus (BKV) and John Cunningham virus (JCV) infections in renal transplant recipients (RTR). This retrospective study of 112 RTR investigated the presence of CMV, EBV and polyomaviruses DNA in plasma and/or urine by PCR. The visualization of PCR products was performed by electrophoresis on 2% agarose gel stained with ethidium bromide and photographed under a UV light. The chi-square test was used for statistical analysis. CMV DNA was detected in 14/112 (12.5%), EBV DNA in 4/49 (8.16%), BKV DNA in 10/31 (32.26%) and JCV DNA in 3/31 (9.68%) RTR. These results show that CMV infection is more often present in RTR compared to other investigated viral infections. In the light of these results, molecular testing could be useful in identifying recipients at high risk of symptomatic post-transplant viral infection.

Naïve T Cell-Derived CTL Recognize Atypical Epitopes of CMVpp65 with Higher Avidity Than CMV-Seropositive Donor-Derived CTL – a Basis for Treatment of Post-Transplant Viral Infection by Adoptive Transfer of T Cells From Virus-naïve Donors

Abstract 3002Adoptive transfer of CMV-specific T cells derived from adult CMV-seropositive (CMVpos) donors can effectively restore antiviral immunity after stem cell transplantation. However due to the absence of CMV antigen-specific memory T cells in cord blood (CB) and adult CMV-seronegative (CMVneg) donors, different culture systems are required to generate virus-specific T cells for adoptive transfer. With a novel protocol we have generated CMVpp65-specific T cells from CB and found that 15/15 CB T cell lines recognized atypical epitopes of pp65. We then explored the generation of CMV-specific CTL from CMVneg donors using a GMP-compliant methodology and studied the epitopes recognized. CD45RA+ naive T cells were selected from the peripheral blood of CMVneg donors and stimulated with pp65-Pepmix-pulsed dendritic cells with supplemented with IL-7, IL-12, and IL-15. For subsequent stimulations T cells were stimulated with pp65-Pepmix-pulsed EBV-LCL and IL-15 or IL-2. CMVpp65-specific T cells (CMV-CTL) expanded from 8 of 11 CMVneg donors were primarily CD8+ T cells (mean 71%). Naïve donor CMV-CTL secreted IFN- γ in response to pp65 peptides (mean 224; range: 38–611 SFC/1×105 cells) compared to irrelevant peptides (mean 12;Range 3–37) as measured in Elispot assays and lysed pp65-pulsed target cells (mean :48; range :15–70%) but not negative controls (mean 22; range 4–40%). These CMV-CTL derived from naive (but not memory) T cells recognized only novel and atypical pp65 epitopes (such as the HLA-A2-restricted epitopes LQTGIHVRV and MLNIPSINV) but not the typical HLA-A2-restricted epitope NLVPMVATV as confirmed by ELISPOT and multimer analysis. These results are similar to CB-derived CTL. Analysis of the avidity of naïve donor CTL specific for the atypical CMV epitopes revealed that the 1/2 maximum effective concentration was similar (mean: 600 pM) to CMVpos CTL recognizing typical epitopes (mean: 300 pM), and more avid than CMVpos CTL recognizing atypical epitopes (mean: 4 nM), highlighting the difference between naïve-derived and memory-derived CTL. TCR sequencing performed on T cells specific for typical (CMVpos) and atypical (CMVpos, CMVneg, and CB) epitopes revealed that CMVpos donor CMV-CTL recognizing typical epitopes were markedly more oligoclonal than CTL recognizing the atypical epitopes derived from CB, CMVpos, or CMVneg donors. To address the concern that atypical epitopes might not be naturally presented by CMV-infected cells and therefore not recognized by in vitro generated CTL, we tested whether CMV CTL (from CB, CMVpos, CMVneg) generated using CMV AD169-infected fibroblasts or CMV VR1814-infected DCs would recognize the same epitopes. As before, CMVpos CMV CTL recognized typical epitopes of pp65 while CB and CMVneg CMV CTL recognized only atypical epitopes, suggesting that the epitopes are naturally processed and presented by APCs, and that the atypical epitopes observed are not an artifact of using exogenous antigens like the pp65 Pepmix. Thus, despite their unusual repertoire, T cells derived from CB or CMVneg donors are likely to control CMV infection. These results reveal major differences in the naïve and memory CMV specific T cell repertoire that merits further exploration. Nevertheless, we demonstrated that atypical epitopes are naturally presented by CMV infected cells and we are now evaluating the clinical efficacy of these CTL in recipients of CBT. These studies should determine if naive T cells primed in vitro are able to persist and establish memory and virus protection in vivo. Disclosures:No relevant conflicts of interest to declare.

Adverse events following infusion of T cells for adoptive immunotherapy: a 10-year experience

The Food and Drug Administration (FDA) currently recommends at least 4 h of recipient monitoring after T cell infusions to detect early infusion reactions. Recent catastrophic reactions to 'first-in-man' biologic agents have emphasized the importance of this rule for initial studies of new products. The value of such monitoring for better established agents is less obvious. We reviewed infusion-related adverse events (AE) following administration of ex vivo-expanded T cell products (antigen-specific cytotoxic T lymphocytes, allodepleted T cells, and genetically modified T cells) on investigational new drug (IND) studies in our center. From 1998 to 2008, we infused 381 T cell products to 180 recipients, enrolled on 18 studies, receiving T cells targeting malignancies or post-transplant viral infections. There were no grade 3-4 infusion reactions during initial monitoring or 24-h follow-up. Twenty-four mild (grade 1-2) AE occurred in 21 infusions either during or immediately following infusion (up to 6 h), most commonly nausea and vomiting (10/24, 41.6%), probably because of the dimethyl sulfoxide cryoprotectant, and hypotension (20.8%), attributable to diphenhydramine pre-medication. Twenty-two additional non-severe events were reported within 24 h of infusion, most commonly culture-negative fever, chills and nausea. An increased risk of adverse events was associated with age [incidence rate ratio (IRR) 0.98; 95% confidence interval (CI) 0.96-1.00, P = 0.05], while an increased risk of immediate infusion-related events was higher in patients reporting allergies (IRR 2.72, 95% CI 1.00-7.40, P = 0.05); sex, disease type and T cell source (allogeneic or autologous) had no effect on frequency of adverse events. Infusion of these T cell products was safe in the outpatient setting and associated with no severe reactions, so monitoring for 1 h after infusion is probably sufficient. As many of the AE were attributable to diphenhydramine premedication, a lower dose (0.25 mg/kg) should be selected.

Adverse Events Following Infusion of T Cells for Adoptive Immunotherapy: A 10 Year Experience.

Abstract 3212Poster Board III-149Following administration of ex-vivo expanded T cells, the FDA currently recommends at least 4 hours of recipient monitoring to detect early infusion reactions. Recent catastrophic reactions to “first in man” biological agents have emphasized the importance of this rule for initial studies of new products, but its value for longer established agents is less evident. We have therefore reviewed the incidence and nature of infusion-related adverse events (AEs) associated with administration of ex-vivo expanded T cell products (antigen specific CTLs, allodepleted T cells, and genetically modified T cells) on Investigational New Drug (IND) studies in our center over the last decade. From 1998 to 2008, we infused 381 T cell products to 180 recipients who were enrolled on 18 such studies, receiving T cells targeting malignancies or post-transplant viral infections. The age of these recipients ranged from 9 months to 80 years. Cell doses were protocol specific and ranged from 104/kg up to 3 ×108/m2. Patients were premedicated with diphenhydramine (0.5-1mg/kg) and acetaminophen (10mg/kg up to a maximum of 625mg) prior to infusion. All cellular products were cryopreserved and administered intravenously over 1-15 minutes immediately after thawing. There were no Grade 3-4 infusion reactions during initial monitoring or 24 hour follow-up. Twenty four grade 1-2, non-severe adverse events (AEs) occurred in 21 infusions either during or immediately following infusion (up to 6 hours). The most common AEs were nausea and vomiting (10/24; 41.6%), most likely due to DMSO used in cryopreservation of T cell products, and hypotension (20.8%), attributable to diphenhydramine pre-medication. An additional 22 non-severe events within 24 hours of infusion were reported, the most common of which were fever (with negative blood cultures)/chills/constitutional symptoms (6/22; 27.3%) and nausea/vomiting (4/22; 18.2%) Overall, a total of 46 non-severe adverse events were noted within 24 hours of T cell product infusion (12.56%). A Fisher's exact analysis of all T cell product infusions grouped by patient age, patient ethnicity, or cell source revealed no association with increased risk. T cells from both allogeneic and autologous sources produced similar adverse events in terms of type, frequency, and severity, and allogeneic cells that were mismatched at > 2 HLA antigens had the same AEs as donor T cells matched at 5/6 or 6/6 HLA loci. We further analyzed the data using Poisson regression and the general estimating equation (GEE) model for correlated counts, to seek associations that may have been missed because AEs within a subject may not be statistically independent. By this analysis, we found decreased risks of adverse events in older patients (IRR 0.98; 95% CI 0.96-1.00; p=0.05), and increased risks of immediate (defined as occurring during the monitoring period) infusion-related events in patients reporting allergies (IRR 2.72; 95% CI 1.00-7.40; p=0.05). We thus conclude that infusion of the ex-vivo expanded T cell products used in these studies is a safe procedure associated with no severe reactions, that it is safe in the outpatient setting and that monitoring can be limited to an hour after infusion. As many of the AEs observed were due to diphenhydramine premedication, a lower dose (0.25mg/kg) of this agent may be preferred. DisclosuresNo relevant conflicts of interest to declare.

Pharmacotherapy of post-transplant viral infections

Background: Management of a number of significant viral pathogens in transplant recipients remains challenging. Objectives: To define an optimal antiviral approach to the management of cytomegalovirus (CMV), human herpes virus-6 (HHV-6), Epstein–Barr (EBV)-associated post-transplant lymphoproliferative disorder (PTLD), and polyoma virus-associated nephropathy in transplant recipients. Methods: Clinical trials and existing data regarding use of antiviral agents for these viruses were reviewed to develop evidence-based recommendations for their management. Conclusions: Weighing the current evidence regarding the use of valganciclovir as pre-emptive therapy or prophylaxis, the former approach offers a greater benefit for the overall prevention of CMV disease. Limited data show that prophylaxis with antiviral agents is associated with a reduction in the risk of EBV-associated PTLD. Treatment options for HHV-6 and polyoma virus-associated nephropathy are still limited.

Antibody Targeting of Activated Dendritic Cells Prevents AGVHD and Preserves T Cell Immunity.

AGVHD is a life threatening complication of allogeneic HSCT, initiated by host and donor DC stimulation of donor T lymphocytes. Current AGVHD prophylaxis targets T lymphocytes, compromising anti-viral and therapeutic anti-leukemic responses. The presence of activated blood DC predicts for clinical AGVHD and we predict that a new strategy targeting therapy to activated DC should prevent alloimmune induction of AGVHD but preserve protective T cell immune responses. CD83 is a cell surface molecule expressed by activated DC. Having shown that a rabbit polyclonal antibody to human CD83 (RA83) depletes activated DC and suppresses alloimmune reactions in vitro, we tested the effect of RA83 treatment on T cell immunity in vitro and its ability to prevent human PBMC induced xenogeneic AGVHD in vivo.The effect of RA83 treatment on T cell numbers, proliferation and cytokine secretion in allogeneic MLR was compared with appropriate controls, including Campath-1H. Allogeneic responses in vitro were mirrored in a DC dependent in vivo model of xenogeneic AGVHD, in which 50×106 human PBMC were injected into an irradiated SCID mouse. Human cytokine levels were measured in MLR tissue culture supernatant (TCSN) and mouse serum at the time of sacrifice. Cytotoxic T cell responses to viral antigens (CMV and FMP) were analysed by specific pentamer analysis and Cr51 release assays, prior to and following HLA restricted peptide antigen specific expansion.RA83 was shown to have NK-mediated ADCC capacity. Cellular proliferation in the allogeneic MLR was reduced by both RA83 and Campath-1H treatment (p= 0.004 and 0.01 respectively vs controls) and both antibodies improved mouse survival in the human xenogenic AGVHD model (RA83: 93%, Campath-1H: 100%, p<0.0001). IFN-g was significantly reduced in the TCSN from MLR treated with RA83 (p=0.0391) and in sera taken from RA83 (p=0.0002) and Campath-1H (p=0.0051) treated mice. Serum IL-4 levels were maintained in RA83 and Campath-1H treated mice. The serum levels of IL-5, IL-8 and TNF in mice treated with RA83 were markedly reduced compared to controls (p=0.0256, 0.0025, 0.025, respectively), and the reductions were similar to those seen in Campath-1H treated mice. Similar numbers of T cells were recovered from RA83 treated and control MLR, and both CMV and FMP specific CD8+ T cells were retained. These cells were readily expanded by peptide pulsing and autologous restimulation and had specific cytotoxic activity comparable to control cultures (see figure). In contrast, Campath-1H treatment removed specific anti-viral responses (vs controls: CMV: p<0.00001 and FMP: p=0.0051).Specific antibody to CD83 depletes activated DC in vitro and prevents xenogeneic human DC dependent AGVHD in vivo. This was accompanied by a Th1 to Th2 skewing of the cytokine response. RA83, but not Campath-1H treatment retained normal numbers of T cells and maintained normal cytotoxic responses to common post-transplant viral infections. Depletion of activated DC may be an effective means of AGVHD control, which maintains T cell immunity to life threatening infections and potentially anti-leukaemia responses. [Display omitted]

Cell mediated immunity (CMI) and post transplant viral infections — Role of a functional immune assay to titrate immunosuppression

Cell mediated immunity (CMI) was assessed by the ImmuKnow assay in 12 patients after kidney transplantation, who presented with viral infection. Treatment included lowering of immunosuppression in all cases and antiviral treatment if indicated. The assay was repeated during the follow up. The ImmuKnow assay at time of presentation of viral infections was 56.8 ± 58.2 (range 3–178; median 22) ATP ng/ml. With the clearance of viral infection and lowering of immunosuppression, the assay showed an increase in the level of CMI at 194.5 ± 118.9 (range 53–409; median 150) ATP ng/ml. There was viral clearance or stabilization in all cases and there was no incidence of allograft rejection. The ImmuKnow assay of CMI can be used to titrate initial immunosuppression reduction and its subsequent increase, in patients with viral infection after transplantation.

Modulation of GvHD by suicide-gene transduced donor T lymphocytes: clinical applications in mismatched transplantation

In allogeneic hematopoietic cell transplantation (allo-HCT), donor lymphocytes play a central therapeutic role in both GvL and immune reconstitution. However, the full exploitation of these therapeutic properties is limited by the occurrence of GvHD. Different strategies have been investigated to obtain all the benefits derived from donor lymphocytes while avoiding the risk of GvHD. The genetic engineering of donor lymphocytes with the herpes simplex virus-thymidine kinase (HSV-TK) suicide gene confers the ability to modulate GvHD by invivo ganciclovir-induced elimination of the transduced cells. The suicide-gene strategy has applications in both donor lymphocyte infusion (DLI) for disease relapse and in add-back infusions after T-cell depleted allo-HCT. TK cell DLI resulted in anti-tumor activity in a relevant proportion of treated patients. Haplo-identical stem cell transplantation (haplo-HCT) is a promising therapeutic option for patients with high risk hematologic malignancies lacking an HLA-matched donor. However, the profound T-cell depletion required to overcome the risk of lethal GvHD has been associated with a marked delayed T-cell recovery with a prolonged risk of post-transplant viral, fungal and other opportunistic infections. TK cell add-backs efficiently promote early immune reconstitution after haplo-HCT and prevent disease relapse, providing a unique tool for the control of GvHD. The genetic manipulation of donor lymphocytes with a suicide gene is a promising strategy to increase feasibility and safety of allo-HCT.

Immunological aspects of unrelated bone marrow transplantation: alloreactivity and immunoreconstitution

The main complications after bone marrow transplantation (BMT) are graft versus host disease (GvHD), post-transplant viral infections and disease relapse. The underlying causes of these problems are the degree of HLA matching between donor and patient and the rate of immune reconstitution.