A2 Donors Research Articles

Successful A2 to O Simultaneous Liver and Kidney Transplantation in the Setting of Pre-operative Positive HLA Crossmatch: A Case Report

Simultaneous liver and kidney transplantation (SLKT) is possible for patients with high donor-specific HLA antibodies or with A2 donors to O recipients with high A2 titers. We report the first case of SLKT in a highly sensitized O recipient with organs from an A2 donor. The recipient is a 59-year-old woman with chronic kidney disease and liver failure due to autoimmune hepatitis and drug-induced liver injury. Immune work-up 8 days pre-transplant demonstrated a negative crossmatch and no HLA antibody (calculated panel reactive antibodies = 0%). Anti-A2 IgG levels were 512. The donor was a deceased 24-year-old man. One day before transplantation, serum from the recipient showed a significant increase in antibody reactivity (calculated panel reactive antibodies = 100%) attributable to blood product transfusion and memory response from previous pregnancies. Consequently, a crossmatch was positive for T and B cells with two newly detected HLA antibodies against the donor's antigens. On the day of surgery, the liver was transplanted first. Six hours and 37 minutes later, a repeat flow crossmatch was negative; donor-specific antibodies (DSAs) fell below the positive threshold, and anti-A2 IgG titer fell to 256. Thus, the kidney was transplanted after basiliximab induction therapy. Seven days post-transplant, non-donor-specific HLA antibodies were present but DSAs remain negative. The patient was discharged on postoperative day 57 with no signs of rejection at 4 months. This case illustrates a rapid and prolonged reduction in antibody titers (HLA and ABO) after SLKT. SLKT is feasible in patients with both DSA and high anti-A2 titer.

P‐IG‐35 | Our Experience in Using A1 Lectin for Solid Organ Transplant Triaging Between Group A1 and Non‐Group A1 Donors

P‐IG‐35 | Our Experience in Using A1 Lectin for Solid Organ Transplant Triaging Between Group A1 and Non‐Group A1 Donors

ABO Genotyping finds more A2 to B kidney transplant opportunities than lectin-based subtyping

ABO compatibility is important for kidney transplantation, with longer waitlist times for blood group B kidney transplant candidates. However, kidneys from non-A1 (eg, A2) subtype donors, which express less A antigen, can be safely transplanted into group B recipients. ABO subtyping is routinely performed using anti-A1 lectin, but DNA-based genotyping is also possible. Here, we compare lectin and genotyping testing. Lectin and genotype subtyping was performed on 554 group A deceased donor samples at 2 transplant laboratories. The findings were supported by 2 additional data sets of 210 group A living kidney donors and 124 samples with unclear lectin testing sent to a reference laboratory. In deceased donors, genotyping found 65% more A2 donors than lectin testing, most with weak lectin reactivity, a finding supported in living donors and samples sent for reference testing. DNA sequencing and flow cytometry showed that the discordances were because of several factors, including transfusion, small variability in A antigen levels, and rare ABO∗A2.06 and ABO∗A2.16 sequences. Although lectin testing is the current standard for transplantation subtyping, genotyping is accurate and could increase A2 kidney transplant opportunities for group B candidates, a difference that should reduce group B wait times and improve transplant equity.

Discrepant subtyping of blood type A2 living kidney donors: Missed opportunities in kidney transplantation.

Despite the institution of a new Kidney Allocation System in 2014, A2/A2B to B transplantation has not increased as expected. The current Organ Procurement and Transplantation Network policy requires subtyping on two separate occasions, and in the setting of discrepant results, defaulting to the A1 subtype. However, there is significant inherent variability in the serologic assays used for blood group subtyping and genotyping is rarely done. The National Kidney Registry, a kidney paired donation (KPD) program, performs serological typing on all A/AB donors, and in cases of non-A1/non-A1B donors, confirmatory genotyping is performed. Between 2/18/2018 and 9/15/2020, 13.0% (145) of 1,111 type A donors registered with the NKR were ultimately subtyped as A2 via genotyping. Notably, 49.6% (72) of these were subtyped as A1 at their donor center, and in accordance with OPTN policy, ineligible for allocation as A2. Inaccurate A2 subtyping represents a significant lost opportunity in transplantation, especially in KPD where A2 donors can not only facilitate living donor transplantation for O and highly sensitized candidates, but can also facilitate additional living donor transplants. This study highlights the need for improved accuracy of subtyping technique, and the need for policy changes encouraging optimal utilization of A2 donor kidneys.

Impact of the 2014 kidney allocation system changes on trends in A2/A2B into B kidney transplantation and organ procurement organization reporting of donor subtyping.

The current kidney allocation system (KAS) preferentially allocates kidneys from blood type A2 or A2B (A/A2B) donors to blood type B candidates. We used national data to evaluate center-level performance of A2/A2B to B transplants, and organ procurement organization (OPO) reporting of type A or AB donor subtyping, in 5-year time periods prior to (2009-2014) and following (2015-2019) KAS implementation. The number of centers performing A2/A2B to B transplants increased from 17 pre-KAS to 76 post-KAS, though this still represents only a minority of centers (7.3% pre-KAS and 32.6% post-KAS). For high-performing centers, the median net increase in A2/A2B to B transplants was 19 cases (range -2-72) per center in the 5 years post-KAS. The median net increase in total B recipient transplants was 21 cases (range -17-119) per center. Despite requirements for performance of subtyping, in 2019 subtyping was reported on only 56.4% of A/AB donors. This translates into potential missed opportunities for B recipients, and even post-KAS up to 2322 A2/A2B donor kidneys may have been allocated for transplantation as A/AB. Further progress must be made both at center and OPO levels to broaden implementation of A2/A2B to B transplants for the benefit of underserved recipients.

Kidney transplantation across minor ABO incompatibility: the use of A2 to B transplants.

On 4 December 2014, the new kidney allocation system (KAS) went into effect. As part of this system, UNOS approved for the first time a national system with a specific mechanism affording priority to allocate kidneys across so-called 'minor ABO incompatibility' from blood group A2 donors into blood group B recipients. This significantly increased the number of such transplants done and the opportunities to learn about the specifics of such transplants. A2 to B transplants have been demonstrated to be well tolerated, effective, and cost-effective ways of addressing disparities in the allocation system. Further data about the use of anti-A titers and the limits to successful transplant have better defined the bounds of who can benefit from such transplants. The success thus far with A2 to B transplants should increase comfort and acceptance of the allocation policy changes and we should see further increases in centers willing to use such transplants to better address inequalities in the system.

New rules of ABO-compatibility in kidney transplantation

ABO compatibility rules in kidney transplantation have been deeply modified with the possibility of ABO-incompatible transplantation. The recipient has to be prepared in the days preceding surgery with an objective of ABO antibody titers of 1/8 or less. This is obtained through a procedure including antibody removal, rituximab and IV immunoglobulins alone or in association according to the initial titer. All ABO combinations are possible. Due to the preparation of the recipient, living related transplantation has been first carried out but ABO-incompatible transplantation from a deceased donor is becoming common practice in some countries (A2 or A2B donor to a B recipient). Lower uncensored graft survival has been reported by some studies but not when ABO-incompatible kidney transplantations were compared with matched ABO-compatible ones. The infectious risk in the perioperative period, consequence of higher immunosuppression, raises concern. The interlaboratory variability in hemagglutination anti-A/B assays remains an important question among cohort studies which leads to development of new tests. ABO-incompatible transplantation is associated with a rare process, accommodation, that is well known in xenotransplantation and according to which, the transplant is protected against the consequences of ABO antibody binding. In human kidney ABO-incompatible transplantation, few studies are available but suggest that this protection against the post-transplant antibody rebound might be mediated by the expression of anti-complement molecules by endothelial cells.

P106 LinkSēq for ABO, a molecular based typing solution for the ABO blood group

Aim ABO-incompatible (ABOi) organs have been successfully transplanted from A2 donors into B recipients, especially when the recipient’s anti-A titers are reduced. Laboratories typically use serological methods to perform ABO typing. However, serology has significant limitations including (i) recently transfused patients may exhibit mixed field agglutination and (ii) both forward and reverse typing must be performed, but may yield discordant results. These limitations are most problematic with phenotypes involving weakly expressed antigens and ABO subgroups (i.e. A2). However, current ABO subgrouping methods using anti-A1 lectin have limitations: they only indirectly determine A2, and typically include a gray zone reactivity range for which subgroups cannot be reliably called. A combination of genotyping solutions (SSP, sequencing, etc) can be used for ABO subgrouping, but these methods are time- and labor-consuming, and require interpretation by subject matter experts. Methods The Thermo Fisher Scientific solution is based on its LinkSēq real-time PCR technology, which was developed over 10 years ago for genotyping the complex Human Leukocyte Antigen (HLA) system. LinkSēq ABO analyzes 19 reactions that identify multiple relevant SNPs located within the ABO gene. We evaluated this solution by analyzing 40 archived DNA samples, including blood blank samples for which serotyping failed or produced discordant results, and samples from deceased solid organ donors for comparison with A1 lectin testing. Results Genotyping results generated by LinkSēq were 100% concordant with typing obtained by traditional methodologies. In two cases, serology couldn’t provide conclusive results and typing had to be reflexed to lectin tests or SBT. LinkSēq overcomes the major challenges of molecular typing by providing a robust, automated approach that increases laboratory productivity and reduces turn-around time. With less than 10 min of hands-on set-up, no further operator intervention with reagents, and SureTyper software fully automating all analysis, LinkSēq delivers genotyping and predicted phenotyping results in approximately 90 min. Conclusions We conclude that LinkSēq can provide a simple, effective and robust method for ABO typing including accurate A2 subgrouping.

P142 Pronase treatment can cause false positive T-cell flow cytometry crossmatches in patients with autoimmune diseases: two clinical cases

Aim Pronase treatment of lymphocytes for flow cytometry crossmatching is used to reduce non-specific B-cell reactivity due to the binding of immune complexes to Fc receptors. However, pronase has been shown to produce false-positive T-cell crossmatches in patients with HIV. We have also encountered this phenomenon with patients suffering from autoimmune diseases. In two cases, the observed T-cell reactivity decreased significantly when sera were crossmatched against unpronased cells. Methods Crossmatches were performed according to standard flow cytometry protocols. Antibodies were assessed with One Lambda Luminex single antigen with a positive cutoff of 2000 MFI. Results Case 1 is a 15 year old African-American male listed for kidney transplant. He has a primary diagnosis of SLE and no sensitization history. Pre-transplant medication history is notable for prednisone and cyclosporine. Sera were crossmatched against pronased deceased donor cells, with T-cell positive results in the absence of DSA. This reactivity disappeared when the crossmatch was repeated with unpronased cells. Case 2 is a 40 year old African-American female listed for kidney/pancreas transplant. She has a primary diagnosis of type 1 diabetes and a sensitization history of 2 pregnancies and moderate transfusions, none recent. Pre-transplant medication history does not include any immunoactive regimens. She is mildly sensitized to Class I and not sensitized to Class II. Sera across several years exhibited positive T-cell crossmatches against multiple cells of type A2. She has A2 antibodies with low titers (2600 MFI). No other DSA was involved. T-cell reactivity was reduced to negative ranges when unpronased cells from A2 donors were used. Conclusions In both cases, auto flow cytometry crossmatches were negative. Therefore, autoreactive antibodies recognizing cryptic epitopes that might be exposed after pronase treatment does not fully explain these results. Neither patient received rituximab at any time. Patients suffering autoimmune diseases may exhibit false positive T-cell crossmatches against pronased cells, in the same manner that has been documented for HIV patients. This reactivity is not attributable to DSA and disappears or significantly decreases when crossmatching is performed with unpronased cells.

P123 Anti-A titer method comparison

Aim To determine an appropriate testing method to evaluate the anti-A titer in blood group B renal transplant waitlist patients to qualify for consideration of blood group A2 (A subgroup) donors. UNOS has established a maximum anti-A titer of 8 to qualify for an A to B kidney. Methods A review of methods in use at transplant centers performing ABO incompatible kidney transplants identified four categories of method variation. The four categories were: • Dithiothreitol (DTT) treatment of serum vs. no DTT treatment • Direct agglutination vs. Indirect agglutination (anti-human globulin enhancement) ∘ Direct = Room Temperature Test Tube or MTS-Gel buffer card ∘ Indirect = Anti-IgG Test Tube or MTS-Gel anti-IgG card • Test Tube method vs. MTS-Gel microcolumn method • A1 target cells vs. A2 target cells Standard commercial blood bank reagents were used for all testing. The same technologist performed all testing. Ten blood group B patients from the kidney transplant waitlist were tested using 8 different methods. After choosing the preferred variable for each of the first three categories, 15 group B potential recipients were tested comparing A1 vs. A2 target cells. Results The categories of Test Tube vs. MTS-Gel and Direct vs. Indirect agglutination had little impact on titers. Pretreatment of serum with DTT provided qualifying titers for three times as many patients as using serum not treated with DTT. DTT pretreatment of serum was chosen along with the indirect agglutination method to optimize detection of IgG anti-A. Using the DTT – Indirect – MTS Gel titer method, comparing A1 vs. A2 target cells with 15 samples showed the choice of target cells also impacted titers. 8 of 15 patients had a 3-fold or greater titer increase using A1 cells compared to A2 cells. 11 of 15 patients (73%) had a qualifying titer with A1cells, compared to 100% with A2 cells. Conclusions Use of DTT treated serum and A2 cells were associated with the lowest anti-A titers. Efforts to establish acceptable method specific titer limits are encouraged.

P124 Best target for anti-A titer determination: A1 or A2 cells

Aim To determine the appropriate target cell for assessment of anti-A titer in blood group B kidney transplant patients waiting for a deceased donor and qualify for blood group A2 (A subgroup) donors according to OPTN/UNOS guidelines. Methods 248 sera samples collected from 57 blood group B candidates (56% male, 79% African American) and tested after DTT treatment. Titers were done using A1 and A2 reagent target cells using the MTS Gel anti-IgG card method. Standard commercial blood bank reagents were used for all testing (2 donors per lot of A1 or A2 cells). The same technologist performed all titers. The titer for eligibility is ⩽ 8. Results 37 patients were eligible (titer ⩽ 8) with either A1 or A2 cells. 20 patients (35%) shown below had titers from 16 up to 128 with A1 cells. 2(4%) patients had a titer >8 with A2 cells. Of these 20 patients, the cPRA varied from 0–100% and was not correlated with anti-A titer. Sex and race was also not correlated with an anti-A titer ⩾ 8. Conclusions Patient eligibility may vary considerably depending on the target cell used. Additional clinical studies will be required to determine the optimum approach.

Impact of the New Kidney Allocation System A2/A2B--> B Policy on Access to Transplantation among Minority Candidates

Introduction Blood group B kidney transplant candidates, many of whom represent ethnic minorities, have historically had diminished access to deceased donor kidney transplantation (DDKT). However, due to the decreased antigenicity of the blood group subtype A2, A2 incompatible (A2i) transplantation can be achieved successfully without the need for additional immunomodulation. Therefore, in an effort to address the ethnic and blood group disparity in access to DDKT, the new national kidney allocation system (KAS) implemented in December 2014, preferentially allocates deceased donor kidneys from blood group A2 and A2B donors to blood group B recipients. To date, no study has examined the impact of KAS on A2i DDKT rates overall for blood group B recipients or among ethnic minorities. Materials and Methods A case-control study of adult blood group B DDKT recipients was performed from 2013 through 2017, as reported to the Scientific Registry of Transplant Recipients. The likelihood of A2i DDKT was compared from the pre-KAS period (1/1/2013-12/3/2014) to the post-KAS period (12/4/2014-2/28/2017) using multivariate logistic regression. Results Following the implementation of KAS, there was a 4.9-fold increase in the likelihood of A2i DDKT for blood group B recipients, compared to the pre-KAS period (OR 4.92, 95% CI: 3.67-6.60). Likewise, the number of transplant centers that had performed one or more A2/A2B to B DDKT increased from 6.9% in the pre-KAS period, to 26.4% post-KAS. However, compared to White blood group B recipients, there was no change in the likelihood of A2i DDKT in the post-KAS era among the following minority groups: African Americans (aOR 0.90, 95% CI: 0.43-1.86 pre-KAS, aOR 0.91, 95%CI: 0.69-1.21 post-KAS); Asians (aOR 1.23, 95% CI 0.49-3.04 pre-KAS, aOR 1.02 95%CI 0.68-1.53 post-KAS); and Hispanics (aOR 1.32, 95% CI 0.51-3.42 pre-KAS, aOR 1.38, 95% CI 0.94-2.03 post-KAS)(Table). Conclusion Although the implementation of KAS has resulted in an increase in A2i DDKT for blood group B recipients, the likelihood of A2i DDKT among minorities, relative to Whites, was not improved. Further discussion regarding A2/A2B --> B policy revisions aimed to increase access to DDKT for ethnic minorities is warranted.American Society of Transplant Surgeons (ASTS) Diversity Affairs Committee. National Institutes of Health- National Research Service Award, through Grant Award Number T32 DK007545. Health Resources and Services Administration contract 234-2005-37011C.

Repeat A2 Into B Kidney Transplantation After Failed Prior A2 Into B Transplant: A Case Report

Kidneys from donors with blood type A2 can be successfully transplanted into blood type B and O recipients without the need for desensitization if the recipient's starting anti-A hemagglutinin titer is within an acceptable range. National kidney allocation policy now offers priority for eligible B recipients to receive A2 or A2B deceased donor kidneys, and therefore, the frequency with which A2 or A2B to B transplants will occur is expected to increase. The precise mechanisms by which antibody-mediated rejection is averted in these cases despite the presence of both circulating anti-A antibody and expression of the A2 antigen on the graft endothelium are not known. Whether this process mirrors proposed mechanisms of accommodation, which can occur in recipients of ABO incompatible transplants, is also not known. Repeated exposure to mismatched antigens after retransplantation could elicit memory responses resulting in antibody rebound and accelerated antibody-mediated rejection. Whether this would occur in the setting of repeated A2 donor exposure was uncertain. Here we report the case of a patient with history of a prior A2 to B transplant which failed owing to nonimmunologic reasons; the patient successfully underwent a repeat A2 to B transplant. Neither rebound in anti-A2 antibody nor clinical evidence of antibody-mediated rejection were observed after the transplant. Current kidney allocation will likely enable more such transplants in the future, and this may provide a unique patient population in whom the molecular mechanisms of incompatible graft accommodation may be investigated.

Kidney exchange transplantation current status, an update and future perspectives.

Kidney exchange transplantation is well established modality to increase living donor kidney transplantation. Reasons for joining kidney exchange programs are ABO blood group incompatibility, immunological incompatibility (positive cross match or donor specific antibody), human leukocyte antigen (HLA) incompatibility (poor HLA matching), chronological incompatibility and financial incompatibility. Kidney exchange transplantation has evolved from the traditional simultaneous anonymous 2-way kidney exchange to more complex ways such as 3-way exchange, 4-way exchange, n-way exchange,compatible pair, non-simultaneous kidney exchange,non-simultaneous extended altruistic donor, never ending altruistic donor, kidney exchange combined with desensitization, kidney exchange combined with ABO incompatible kidney transplantation, acceptable mismatch transplant, use of A2 donor to O patients, living donor-deceased donor list exchange, domino chain, non-anonymous kidney exchange, single center, multicenter, regional, National, International and Global kidney exchange. Here we discuss recent advances in kidney exchanges such as International kidney exchange transplantation in a global environment, three categories of advanced donation program, deceased donors as a source of chain initiating kidneys, donor renege myth or reality, pros and cons of anonymity in developed world and (non-) anonymity in developing world, pros and cons of donor travel vs kidney transport, algorithm for management of incompatible donor-recipient pairs and pros and cons of Global kidney exchange. The participating transplant teams and donor-recipient pairs should make the decision by consensus about kidney donor travel vs kidney transport and anonymity vs non-anonymity in allocation as per local resources and logistics. Future of organ transplantation in resource-limited setting will be liver vs kidney exchange, a legitimate hope or utopia?

A2 liver transplantation across the ABO barrier: Increasing options in the donor pool?

A2 liver transplantation across the ABO barrier: Increasing options in the donor pool?

P047 Stability of anti-A2 blood group subtype titers among blood group B candidates

Aim Kidney allocation based on blood type inadvertently disadvantages ABO B blood group candidates due to their disproportionate representation on the waitlist. To mitigate this situation, OPTN/UNOS modified the allocation system such that group B candidates could receive kidneys from group A2 or A2B donors if their anti-A titers are Methods Anti-A titer information and candidate demographics were reviewed from blood bank records. Patients included in the study were group B, renal allograft candidates who had ⩾2 anti-A titers performed between January 2011 and December 2014. An anti-A titer of >1:8 excluded a group B candidate from receiving an out of group allograft. Variability in titers was assessed by delta dilution change between assays. Results Anti-A titers were assessed on 193 group B, renal allograft candidates with ⩾2 anti-A titers. Following the first titer, 50 patients (26%) were ineligible (i.e.,titer >1:8). Of the remaining 143 patients, 19 (13%) became ineligible following a second titer reaching >1:8. Forty patients (28%) had no delta dilution change between titers and 72 (50%) had a titer change that never reached >1:8. Only 12 patients (6% of total) experienced a titer change that affected eligibility after the second test. Conclusions Although the majority of patients experience some variability in their anti-A titers over time, in most cases the variability does not affect their eligibility to receive an out of blood group renal allograft. Furthermore, the likelihood of a titer change affecting eligibility after two tests is limited to a small subset of patients. Our data suggest that testing of anti-A titers more than twice may not be necessary to effectively monitor recipient eligibility.

A2 to B Blood Type Incompatible Deceased Donor Kidney Transplantation in a Recipient Infected with the Human Immunodeficiency Virus: A Case Report

BackgroundWith the introduction of the Kidney Allocation System in the United States in December 2014, transplant centers can list eligible B blood type recipients for A2 organ offers. There have been no prior reports of ABO incompatible A2 to B deceased donor kidney transplantation in human immunodeficiency virus-positive (HIV+) recipients to guide clinicians on enrolling or performing A2 to B transplantations in HIV+ candidates. We are the first to report a case of A2 to B deceased donor kidney transplantation in an HIV+ recipient with good intermediate-term results. Methods and ResultsWe describe an HIV+ 39-year-old African American man with end-stage renal disease who underwent A2 to B blood type incompatible deceased donor kidney transplantation. Prior to transplantation, he had an undetectable HIV viral load. The patient was unsensitized, with his most recent anti-A titer data being 1:2 IgG and 1:32 IgG/IgM. Induction therapy of basiliximab and methylprednisolone was followed by a postoperative regimen of plasma exchange, intravenous immunoglobulin, and rituximab with maintenance on tacrolimus, mycophenolate mofetil, and prednisone. He had delayed graft function without rejection on allograft biopsy. Nadir serum creatinine was 2.0 mg/dL. He continued to have an undetectable viral load on the same antiretroviral therapy adjusted for renal function. ConclusionsTo our knowledge, this is the first report of A2 to B deceased donor kidney transplantation in an HIV+ recipient with good intermediate-term results, suggesting that A2 donor kidneys may be considered for transplantation into HIV+ B-blood type wait list candidates.

P077 Anti-A titers in ABO incompatible transplantation – An OPO’S experience

Aim The UNET system allows blood type B patients to receive blood type A2 or A2B donor kidneys. To qualify for the program, patients must satisfy titer criteria set by the transplant center. We developed protocols for these types of transplants. Literature states “perform Anti-A titer” and does not differentiate the target sub-group cell to use for titer. We hypothesize that since A2 cells express weaker antigenicity than A1 cells, testing A2 titers would be more representative of the clinical situation and be adequate to ensure a safe transplant. Our aim is to validate the use of Anti-A2 titers for the purpose of A2 or A2B donor kidney transplants for B recipients. Methods Patient titers were performed using donor red blood cells from A2 donors and reagent A2 control cells using the gel method. Sub-grouping of donor’s A blood type was determined. Titers and scores were determined for both IgM and IgG Anti-A2. Post- transplant outcomes were analyzed. Pre- and post- transplant titers were performed, as well as the creatinine level one month post- transplant, and the most recent creatinine level as of May 1, 2016. We also looked at the average Anti-A1 titers as compared to the average Anti-A2 titers of 63 patients. Results Download : Download high-res image (1MB) Download : Download full-size image Average A1 and A2 Titer and Score of 63 Recipients 1. A1 Pre-titer IgM was 3.0 × higher than A2 Pre-titer IgM. 2. IgM score of A1 was 1.6 × higher than IgM score of A2. 3. A1 Pre-titer IgG was 4.3 × higher than A2 Pre-titer IgG. 4. IgG score of A1 was 2.1 × higher than IgG score of A2. Conclusions Our preliminary results suggest that performing Anti-A2 titers is an effective way of measuring the potential blood group B recipient’s risk to receiving a blood group A2 or A2B deceased donor kidney. Furthermore, we suggest that using a blood group B patients Anti-A1 titer to qualify him/her for this “A2/ A2B donor to B recipient “ program will unnecessarily eliminate many patients from receiving a successful transplant. To date 20 patients have been successfully transplanted using this protocol. Detailed outcome data is pending on the additional 12 recipients.

Role of the MHC restriction during maturation of antigen-specific human T cells in the thymus.

In the thymus, a T-cell repertoire able to confer protection against infectious and noninfectious agents in a peptide-dependent, self-MHC-restricted manner is selected. Direct detection of Ag-specific thymocytes, and analysis of the impact of the expression of the MHC-restricting allele on their frequency or function has never been studied in humans because of the extremely low precursor frequency. Here, we used a tetramer-based enrichment protocol to analyze the ex vivo frequency and activation-phenotype of human thymocytes specific for self, viral and tumor-antigens presented by HLA-A*0201 (A2) in individuals expressing or not this allele. Ag-specific thymocytes were quantified within both CD4CD8 double or single-positive compartments in every donor. Our data indicate that the maturation efficiency of Ag-specific thymocytes is poorly affected by HLA-A2 expression, in terms of frequencies. Nevertheless, A2-restricted T-cell lines from A2(+) donors reacted to A2(+) cell lines in a highly peptide-specific fashion, whereas their alloreactive counterparts showed off-target activity. This first ex vivo analysis of human antigen-specific thymocytes at different stages of human T-cell development should open new perspectives in the understanding of the human thymic selection process.

CD123 redirected multiple virus-specific T cells for acute myeloid leukemia

Hematopoietic stem cell transplantation (HSCT) has been increasingly used as a curative treatment for acute myeloid leukemia (AML). However, relapse rates after HSCT in complete remission (CR) are reported between 30% and 70%. In addition, numerous studies suggested that secondary viral infection from a variety of viruses including Epstein-Barr virus (EBV), adenovirus (Adv), and cytomegalovirus (CMV) are among the most common causes of death post-HSCT. Currently, chimeric antigen receptor (CAR)-based T cells have been developed to treat AML in clinical studies, while virus-specific cytotoxic T cells (VST) have been proven to be able to effectively prevent or treat viral infection after HSCT. Thus it would be desirable to develop T cells with the ability of simultaneously targeting AML relapse and viral infection. In this article, we now describe the generation of VST cells that are engineered to express CAR for a specific AML cell-surface antigen CD123 (CD123-CAR-VST). Using Dendritic cells (DCs) pulsed with EBV, Adv, and CMV peptides as sources of viral antigens, we generated VST from A2 donor peripheral mononuclear cells (PBMC). VST were then transduced with retroviral vector encoding CD123-CAR to generate CD123-CAR-VST. We demonstrated that CD123-CAR-VST recognized EBV, Adv, and CMV epitopes and had HLA-restricted virus-specific cytotoxic effector function against EBV target. In addition, CD123-CAR-VST retained the specificity against CD123-positive AML cell lines such as MOLM13 and THP-1 in vitro. Thus our results suggested that CD123-CAR-VST might be a valuable candidate to simultaneously prevent or treat relapse and viral infection in AML HSCT recipients.