Chimeric HLA antibody receptor T cells for targeted therapy of antibody-mediated rejection in transplantation

Chimeric anti-HLA antibody receptor engineered human regulatory T cells suppress alloantigen-specific B cells from pre-sensitized transplant recipients

Organ transplantation is a lifesaving procedure, with 50,000 transplants happening every year in the United States. However, many patients harbor antibodies and B cells directed against allogeneic human leukocyte antigen (HLA) molecules, notably HLA-A2, greatly decreasing their likelihood of receiving a compatible organ. Moreover, antibody-mediated rejection is a significant contributor to chronic transplant rejection. Current strategies to desensitize patients non- specifically target circulating antibodies and B cells, resulting in poor efficacy and complications. Regulatory T cells (Tregs) are immune cells dedicated to suppressing specific immune responses by interacting with both innate and adaptive immune cells. Here, we genetically modified human Tregs with a chimeric anti-HLA antibody receptor (CHAR) consisting of an extracellular HLA-A2 protein fused to a CD28-CD3zeta intracellular signaling domain, driving Treg activation upon recognition of anti-HLA-A2 antibodies on the surface of alloreactive B cells. We find that HLA-A2 CHAR Tregs get activated specifically by anti-HLA-A2 antibody-producing cells. Of note, HLA-A2 CHAR activation does not negatively affect Treg stability, as measured by expression of the Treg lineage transcription factors FOXP3 and HELIOS. Interestingly, HLA-A2 CHAR Tregs are not cytotoxic towards anti-HLA-A2 antibody-producing cells, unlike HLA-A2 CHAR modified conventional CD4 + T cells. Importantly, HLA-A2 CHAR Tregs recognize and significantly suppress high affinity IgG antibody production by B cells from HLA-A2 sensitized patients. Altogether, our results provide proof-of-concept of a new strategy to specifically inhibit alloreactive B cells to desensitize transplant recipients.

Depletion of alloreactive B cells by drug-resistant chimeric alloantigen receptor T cells to prevent transplant rejection

Antibody-mediated rejection (AMR) remains a major complication after solid organ transplantation (SOT). Current treatment options are inefficient and result in drastic impairment of the general immunity. To selectively eliminate responsible alloreactive B cells characterized by anti-donor-HLA B cell receptors (BCRs), we generated T cells overcoming rejection by antibodies (CORA-Ts) engineered with a novel chimeric receptor comprising a truncated donor-HLA molecule as antigen recognition domain. As proof-of-concept, CORA receptors based on HLA-A∗02 were developed. In co-cultures with anti-HLA-A∗02 B cell lines, CORA-Ts were specifically activated, released pro-inflammatory mediators, and exhibited strong cytotoxicity resulting in an effective reduction of anti-HLA-A∗02 antibody release. Significant reduction of growth of an anti-HLA-A∗02 B cell line could be confirmed using an in vivo mouse model. Modification of the CORA receptor effectively abrogated T cell binding, thereby avoiding T cell sensitization. Additionally, using CRISPR-Cas9-mediated knockout of the FKBP12 gene, CORA-Ts were able to resist immunosuppressive treatment with tacrolimus, thereby allowing high efficiency in transplant patients. Our results demonstrate that CORA-Ts are able to specifically eliminate alloreactive, anti-HLA B cells, thus selectively preventing anti-HLA antibody release even under immunosuppressive conditions. This suggests CORA-Ts as potent approach to combat AMR and improve long-term graft survival in SOT patients while preserving their overall B cell immunity.

Antibody-mediated rejection diagnosed in early protocol biopsies in high immunological risk kidney transplant recipients

BACKGROUND

Renal transplant recipients with donor-specific anti-HLA antibodies are at an increased risk of antibody-mediated rejection (ABMR). Early protocolized renal biopsies may serve as a strategy to improve diagnosis in this patient population.

METHODS

We evaluated 155 highly sensitized renal transplant recipients with cPRA class I + II >90% pre-transplant from 2015 to 2022. Patients with protocol biopsies within the first 2 weeks post-transplant were included.

RESULTS

A total of 122 patients were included in the study. Of these, 13 (10.6%) were diagnosed with very early antibody-mediated rejection (veABMR) within the first 2 weeks post-transplant. This corresponds to 52% (13/25 patients) of all ABMR cases reported during the follow-up of this population. The graft survival rates at 1 and 3 years were significantly lower in patients with veABMR (P < .001) compared with patients without rejection in the early protocol biopsy. In terms of severity, the veABMR cohort exhibited a hazard ratio (HR) of 10.33 (95% confidence interval 3.23-33.06, P < .001) for graft failure. The presence of donor-specific antibodies class II on the day of transplantation and a higher percentage of eplet mismatch (EpMM), particularly EpMM DQA1, correlated with the development of veABMR.

CONCLUSION

Early protocol biopsies play a pivotal role in the early detection of veABMR in high-risk immunological patients. Patients with veABMR face significant risks of graft loss, despite early treatment of rejection.

Cars pick up another passenger: Organ transplantation

With over 30,000 patients having received CAR T cells as a treatment for malignancy, our experience in oncology has facilitated numerous efforts to adapt the CAR therapeutic platform for diseases and conditions beyond cancer. Recognition of their efficacy, where traditional small molecule or biologic therapies fail, has spurred multiple efforts leveraging CAR T cells for immune modulation in the setting of organ/tissue transplantation. In the present review, we discuss CAR T cell approaches that are currently under development, to target both humoral and cellular alloimmunity. These include CAR T platforms repurposed from oncology and autoimmune diseases, as well as ones designed specifically to target alloimmunity in transplant. We also present important challenges and application considerations that will need to be addressed before we can expect successful clinical translation. Finally, we highlight a few of the exciting advances currently in development that are likely to pave a smoother path to translating CAR T cell therapies into transplant patients.

Chimeric HLA antibody receptor T cell therapy for humoral transplant rejection

Antibody-mediated rejection (ABMR) is a significant obstacle to achieving optimal long-term outcomes after solid organ transplantation. The presence of donor-specific antibodies (DSAs), particularly against human leucocyte antigen (HLA), increases the risk of allograft rejection and subsequent graft loss. No effective treatment for ABMR currently exists, warranting novel approaches to target the HLA-specific humoral alloimmune response. Cellular therapies may hold promise to this end. According to publicly available sources as of now, three independent laboratories have genetically engineered a chimeric HLA antibody receptor (CHAR) and transduced it into human T cells, based on the demonstrated efficacy of chimeric antigen receptor T cell therapies in malignancies. These CHAR-T cells are designed to exclusively eliminate B cells that produce donor-specific HLA antibodies, which form the cornerstone of ABMR. CHAR technology generates potent and functional human cytotoxic T cells to target alloreactive HLA-specific B cells, sparing B cells with other specificities. Thus CHAR technology may be used as a selective desensitization protocol and to treat ABMR after solid organ transplantation.

Immunotherapy targeting B cells and long-lived plasma cells effectively eliminates pre-existing donor-specific allo-antibodies

Pre-existing anti-human leukocyte antigen (HLA) allo-antibodies constitute a major barrier to transplantation. Current desensitization approaches fail due to ineffective depletion of allo-specific memory B cells (Bmems) and long-lived plasma cells (LLPCs). We evaluate the efficacy of chimeric antigen receptor (CAR) T cells targeting CD19 and B cell maturation antigen (BCMA) to eliminate allo-antibodies in a skin pre-sensitized murine model of islet allo-transplantation. We find that treatment of allo-sensitized hosts with CAR T cells targeting Bmems and LLPCs eliminates donor-specific allo-antibodies (DSAs) and mitigates hyperacute rejection of subsequent islet allografts. We then assess the clinical efficacy of the CAR T therapy for desensitization in patients with multiple myeloma (MM) with pre-existing HLA allo-antibodies who were treated with the combination of CART-BCMA and CART-19 (ClinicalTrials.gov: NCT03549442) and observe clinically meaningful allo-antibody reduction. These findings provide logical rationale for clinical evaluation of CAR T-based immunotherapy in highly sensitized candidates to promote successful transplantation.