Donor CD4 T cells convert mixed to full donor T-cell chimerism and replenish the CD52-positive T-cell pool after alemtuzumab-based T-cell-depleted allo-transplantation

CD52/GPI- T-Cells Are Enriched for Alloreactive Specificity and Predict Acute Graft-Versus-Host-Disease After Stem Cell Transplantation

Alemtuzumab is a CD52-specific lympho-depleting antibody. CD52- T cells emerge under alemtuzumab selection pressure. We sought to investigate the phenotype and function of the CD52- T cell fraction and related their presence to clinical outcome. We obtained longitudinal peripheral blood samples from 67 consecutive patients undergoing allo-HSCT between 2013-2016. Forty-seven patients (70%) had a myeloid disease (acute myelogenous leukemia or myelodysplastic syndrome) whereas 20 patients had lymphoid disease. All patients received in vivo alemtuzumab (10 mg/d from day -5 for 5 days) as part of their conditioning protocol. Sixty-three (94%) received reduced-intensity conditioning chemotherapy, whereas 4 (6%) received a myeloablative regimen. All patients received post-transplantation cyclosporine A for graft-versus-host disease (GVHD) prophylaxis. Six (9%) also received methotrexate, whereas 2 (3%) patients also received mycophenolate mofetil. Overall survival at 2 years was 68%, and relapse-free survival was 48%. Twenty-none percent of patients experienced acute GVHD (grade 2 or above), and 15% developed chronic GVHD. CD52- T cells were detectable in 66 of 67 consecutive patients. CD52- T cells demonstrated low binding of fluorescent aerolysin, indicating downregulation of the glycophosphatidylinositol anchor, although we did not detect any mutations in the PIG-A gene as is typically seen in patients with paroxysmal nocturnal hemoglobinuria. CD52- T cells were almost exclusively CD4+ and exhibited a dominant memory phenotype with only small numbers of CD25+ CD127low Foxp3+ regulatory T cells. CD52- T cells exhibited alloreactive specificity in vitro and have a distinct TCR repertoire to CD52+ T cells. Early after allo-hematopoietic stem cell transplantation, the presence of a significant population of CD52- T cells (comprising >51% of the T cell fraction) was found to be an independent risk factor for acute GvHD. This was confirmed in a validation cohort of 28 patients obtained between 2017-2018. These data suggest that the CD52- T cell fraction may represent a residual "footprint" of an early CD4+ T cell alloreactive response and may have been rescued from alemtuzumab-mediated lysis by antigen engagement in vivo. These data help to delineate the nature of T cell escape from alemtuzumab surveillance and contribute to increasing interest in the importance of CD4+ T cells in alloreactive immune responses, which could help inform immunotherapy protocols.

Mutations in PIGA cause a CD52-/GPI-anchor-deficient phenotype complicating alemtuzumab treatment in T-cell prolymphocytic leukemia

OBJECTIVE

Infusional alemtuzumab followed by consolidating allogeneic hematopoietic stem cell transplantation in eligible patients is considered a standard of care in T-cell prolymphocytic leukemia (T-PLL). Antibody selection against CD52 has been associated with the development of CD52-negative leukemic T cells at time of relapse. Clinical implications and molecular mechanisms underlying this phenotypic switch are unknown.

METHODS

We performed flow cytometry and real-time-PCR for CD52-expression and next generation sequencing for PIGA mutational analyses.

RESULTS

We identified loss of CD52 expression after alemtuzumab treatment in two of 21 T-PLL patients resulting from loss of GPI-anchor expression caused by inactivating mutations of the PIGA gene. One patient with relapsed T-PLL exhibited a single PIGA mutation, causing a CD52-negative escape variant of the initial leukemic cell clone, preventing alemtuzumab-retreatment. The second patient with continued complete remission after alemtuzumab treatment harbored three different PIGA mutations that affected either the non-neoplastic T cell or the mononuclear cell compartment and resulted in symptomatic paroxysmal nocturnal hemoglobinuria. Next generation sequencing of T-PLL cells collected before the initiation of treatment revealed PIGA wild-type sequence reads in all 16 patients with samples available for testing.

CONCLUSION

These data indicate that PIGA mutations were acquired during or after completion of alemtuzumab treatment.

CD52-negative T cells predict acute graft-versus-host disease after an alemtuzumab-based conditioning regimen

Allogeneic haematopoietic stem cell transplantation (HSCT) after a reduced-intensity conditioning (RIC) regimen with fludarabine, melphalan and alemtuzmab is an effective therapy for haematological malignancies. Alemtuzumab, a monoclonal antibody against CD52, a glycosylphosphatidylinositol-anchor-bound surface protein on lymphocytes, depletes T cells to prevent graft-versus-host disease (GVHD). Despite this, acute and chronic GVHD (a/cGVHD) remain life-threatening complications after HSCT. The aim of the present study was to identify parameters to predict GVHD. In 69 patients after HSCT, T-cell subsets were functionally analysed. Reconstitution of CD52^neg T cells and CD52^neg regulatory T cells (Tregs) correlated with onset, severity and clinical course of aGVHD. Patients with aGVHD showed significantly lower levels of CD52^pos T cells compared to patients with cGVHD or without GVHD (P < 0·001). Analysis of T-cell reconstitution revealed a percentage of <40% of CD52^pos CD4^pos T cells or CD52^pos Tregs at day +50 as a risk factor for the development of aGVHD. In contrast, CD52^neg Tregs showed significant decreased levels of glycoprotein A repetitions predominant (GARP; P < 0·001), glucocorticoid-induced TNFR-related protein (GITR; P < 0·001), chemokine receptor (CXCR3; P = 0·023), C-C chemokine receptor type 5 (CCR5; P = 0·004), but increased levels of immunoglobulin-like transcript 3 (ILT3; P = 0·001), as well as a reduced suppressive capacity. We conclude that reconstitution of CD52^neg T cells and CD52^neg Tregs is a risk factor for development of aGVHD.

CD4 Donor Lymphocyte Infusion Can Cause Conversion of Chimerism Without GVHD by Inducing Immune Responses Targeting Minor Histocompatibility Antigens in HLA Class II

Under non-inflammatory conditions HLA class II is predominantly expressed on hematopoietic cells. Therefore, donor CD4 T-cells after allogeneic stem cell transplantation (alloSCT) may mediate graft-vs.-leukemia reactivity without graft-vs.-host disease (GVHD). We analyzed immune responses in four patients converting from mixed to full donor chimerism without developing GVHD upon purified CD4 donor lymphocyte infusion (DLI) from their HLA-identical sibling donor after T-cell depleted alloSCT. In vivo activated T-cells were clonally isolated after CD4 DLI. Of the alloreactive T-cell clones, 96% were CD4 positive, illustrating the dominant role of CD4 T-cells in the immune responses. We identified 9 minor histocompatibility antigens (MiHA) as targets for alloreactivity, of which 8 were novel HLA class II restricted MiHA. In all patients, MiHA specific CD4 T-cells were found that were capable to lyse hematopoietic cells and to recognize normal and malignant cells. No GVHD was induced in these patients. Skin fibroblasts forced to express HLA class II, were recognized by only two MiHA specific CD4 T-cell clones. Of the 7 clones that failed to recognize fibroblasts, two targeted MiHA were encoded by genes not expressed in fibroblasts, presentation of one MiHA was dependent on HLA-DO, which is absent in fibroblasts, and T-cells recognizing the remaining 4 MiHA had an avidity that was apparently too low to recognize fibroblasts, despite clear recognition of hematopoietic cells. In conclusion, purified CD4 DLI from HLA-identical sibling donors can induce conversion from mixed to full donor chimerism with graft-vs.-malignancy reactivity, but without GVHD, by targeting HLA class II restricted MiHA.

Immune Reconstitution after Allogeneic Hematopoietic Stem Cell Transplantation

The timely reconstitution and regain of function of a donor-derived immune system is of utmost importance for the recovery and long-term survival of patients after allogeneic hematopoietic stem cell transplantation (HSCT). Of note, new developments such as umbilical cord blood or haploidentical grafts were associated with prolonged immunodeficiency due to delayed immune reconstitution, raising the need for better understanding and enhancing the process of immune reconstitution and finding strategies to further optimize these transplant procedures. Immune reconstitution post-HSCT occurs in several phases, innate immunity being the first to regain function. The slow T cell reconstitution is regarded as primarily responsible for deleterious infections with latent viruses or fungi, occurrence of graft-versus-host disease, and relapse. Here we aim to summarize the major steps of the adaptive immune reconstitution and will discuss the importance of immune balance in patients after HSCT.

Allo-reactive T cells for the treatment of hematological malignancies

Several mechanisms can be responsible for control of hematological tumors by allo-reactive T cells. Following allogeneic stem cell transplantation (alloSCT) donor T cells recognizing genetic disparities presented on recipient cells and not on donor cells are main effectors of tumor control, but also of the detrimental graft versus host disease (GVHD). Since after transplantation normal hematopoiesis is of donor origin, any T cell response directed against polymorphic antigens expressed on hematopoietic recipient cells but not on donor cells will result in an anti-tumor response not affecting normal hematopoiesis. After fully HLA-matched alloSCT, T cells recognizing polymorphic peptides derived from proteins encoded by genes selectively expressed in hematopoietic lineages may result in anti-tumor responses without GVHD. Due to the high susceptibility of hematopoietic cells for T cell recognition, a low amplitude of the overall T cell response may also be in favor of the anti-tumor reactivity in hematological malignancies. A mismatch between donor and patient for specific HLA-alleles can also be exploited to induce a selective T cell response against patient (malignant) hematopoietic cells. If restricting HLA class II molecules are selectively expressed on hematopoietic cells under non-inflammatory circumstances, allo HLA class-II responses may control the tumor with limited risk of GVHD. Alternatively, T cells recognizing hematopoiesis-restricted antigens presented in the context of mismatched HLA alleles may be used to treat patients with hematological cancers. This review discusses various ways to manipulate the allo-immune response aiming to exploit the powerful ability of allo-reactive T-cells to control the malignancies without causing severe damage to non-hematopoietic tissues.

Outcomes of donor lymphocyte infusion for treatment of mixed donor chimerism after a reduced-intensity preparative regimen for pediatric patients with nonmalignant diseases

Mixed donor chimerism is increasingly common in the pediatric hematopoietic stem cell transplantation (HSCT) setting because of the increased use of reduced-intensity preparative regimens for nonmalignant diseases. Donor lymphocyte infusion (DLI) is potentially useful in the treatment of mixed donor chimerism, but little are data available on the use of DLI in this setting. We conducted a retrospective review of 27 pediatric patients who received DLI for mixed donor chimerism between January 2006 and December 2010 after receiving a preparative regimen of alemtuzumab, fludarabine, and melphalan. Twenty-one patients (78%) were alive at a median of 35 months post-transplant. Seven patients (26%) sustained full donor chimerism after DLI only at a median of 35 months post-HSCT. Nine patients (33%) continued with mixed donor chimerism (median, 38% [range, 18% to 70%]) at a median of 37 months after DLI only. Five patients underwent unconditioned stem cell boosts or second conditioned transplants after no improvement in donor chimerism was seen following DLI. Donor source appeared to contribute to outcomes after DLI; patients with mismatched unrelated donors had earlier first decline in chimerism and timing of first DLI, a higher response rate to DLI, and an increased rate of graft-versus-host disease (GVHD). There was no response to DLI in patients with matched sibling donors. Ten patients, all with improvement in chimerism after DLI, developed acute GVHD after DLI, with 3 having grade III GVHD. Three patients developed chronic GVHD after DLI. These data illustrate the potential efficacy of DLI in the treatment of mixed donor chimerism after a reduced-intensity preparative regimen.

Phase 2 clinical trial of rapamycin-resistant donor CD4+ Th2/Th1 (T-Rapa) cells after low-intensity allogeneic hematopoietic cell transplantation

In experimental models, ex vivo induced T-cell rapamycin resistance occurred independent of T helper 1 (Th1)/T helper 2 (Th2) differentiation and yielded allogeneic CD4(+) T cells of increased in vivo efficacy that facilitated engraftment and permitted graft-versus-tumor effects while minimizing graft-versus-host disease (GVHD). To translate these findings, we performed a phase 2 multicenter clinical trial of rapamycin-resistant donor CD4(+) Th2/Th1 (T-Rapa) cells after allogeneic-matched sibling donor hematopoietic cell transplantation (HCT) for therapy of refractory hematologic malignancy. T-Rapa cell products, which expressed a balanced Th2/Th1 phenotype, were administered as a preemptive donor lymphocyte infusion at day 14 post-HCT. After T-Rapa cell infusion, mixed donor/host chimerism rapidly converted, and there was preferential immune reconstitution with donor CD4(+) Th2 and Th1 cells relative to regulatory T cells and CD8(+) T cells. The cumulative incidence probability of acute GVHD was 20% and 40% at days 100 and 180 post-HCT, respectively. There was no transplant-related mortality. Eighteen of 40 patients (45%) remain in sustained complete remission (range of follow-up: 42-84 months). These results demonstrate the safety of this low-intensity transplant approach and the feasibility of subsequent randomized studies to compare T-Rapa cell-based therapy with standard transplantation regimens.

Favorable outcomes in patients with high donor-derived T cell count after in vivo T cell-depleted reduced-intensity allogeneic stem cell transplantation

Patients with hematologic malignancies were conditioned using a rabbit antithymocyte globulin-based reduced-intensity conditioning regimen for allogeneic stem cell transplantation. Donor-derived CD3(+) cell count (ddCD3), a product of CD3(+) cell chimerism and absolute CD3(+) cell count, when <110/μL at 8 weeks post-stem cell transplantation predicted a high risk of sustained mixed chimerism and relapse. Alternatively, patients with a higher ddCD3 developed graft-versus-host disease more frequently, and when partially chimeric, had higher rates of conversion to full donor chimerism after withdrawal of immunosuppression. Early data from our small cohort of patients indicate that ddCD3 at 8 weeks may be used to guide decisions regarding withdrawal of immunosuppression and administration of donor lymphocyte infusion in partially T cell-depleted reduced-intensity regimens.

Clinical options after failure of allogeneic hematopoietic stem cell transplantation in patients with hematologic malignancies

Disease recurrence is the single most common cause of death after allogeneic or autologous hematopoietic stem cell transplantation (HSCT). Disease status and chemosensitivity at the time of transplantation, as well as the development of graft-versus-host disease (GVHD), are factors known to influence the risk of relapse post-HSCT. Both acute and chronic GVHD have been associated with decreased relapse rates; however, owing to toxicity, overall survival is not consistently improved in these patients. Furthermore, there is a transient period of immunodeficiency after HSCT, which may permit residual malignant cells to proliferate early in the post-transplant course, before the donor immune system can establish a graft-versus-tumor response. Patients who fail an initial HSCT have an extremely poor outcome; therefore, maneuvers to prevent, identify and treat recurrent disease as early as possible in these situations are necessary. Strategies to distinguish graft-versus-tumor from GVHD, to enhance both general and disease-specific immune reconstitution after transplantation, and to increase donor-mediated anti-host immune reactions are being investigated in clinical trials. Single agent nontoxic post-HSCT chemotherapy, cellular therapies and second allogeneic HSCT using reduced intensity regimens are among the modalities under investigation.

Human epidermal Langerhans cells replenish skin xenografts and are depleted by alloreactive T cells in vivo

Epidermal Langerhans cells (LC) are potent APCs surveying the skin. They are crucial regulators of T cell activation in the context of inflammatory skin disease and graft-versus-host disease (GVHD). In contrast to other dendritic cell subtypes, murine LC are able to reconstitute after local depletion without the need of peripheral blood-derived precursors. In this study, we introduce an experimental model of human skin grafted to NOD-SCID IL2Rγ(null) mice. In this model, we demonstrate that xenografting leads to the transient loss of LC from the human skin grafts. Despite the lack of a human hematopoietic system, human LC repopulated the xenografts 6 to 9 wk after transplantation. By staining of LC with the proliferation marker Ki67, we show that one third of the replenishing LC exhibit proliferative activity in vivo. We further used the skin xenograft as an in vivo model for human GVHD. HLA-disparate third-party T cells stimulated with skin donor-derived dendritic cells were injected intravenously into NOD-SCID IL2Rγ(null) mice that had been transplanted with human skin. The application of alloreactive T cells led to erythema and was associated with histological signs of GVHD limited to the transplanted human skin. The inflammation also led to the depletion of LC from the epidermis. In summary, we provide evidence that human LC are able to repopulate the skin independent of blood-derived precursor cells and that this at least partly relates to their proliferative capacity. Our data also propose xeno-transplantation of human skin as a model system for studying the role of skin dendritic cells in the efferent arm of GVHD.

Recipient lymphocyte infusion in MHC-matched bone marrow chimeras induces a limited lymphohematopoietic host-versus-graft reactivity but a significant antileukemic effect mediated by CD8+ T cells and natural killer cells

BACKGROUND

Challenge of MHC-mismatched murine bone marrow chimeras with recipient-type lymphocytes (recipient lymphocyte infusion) produces antileukemic responses in association with rejection of donor chimerism. In contrast, MHC-matched chimeras resist eradication of donor chimerism by recipient lymphocyte infusion. Here, we investigated lymphohematopoietic host-versus-graft reactivity and antileukemic responses in the MHC-matched setting, which is reminiscent of the majority of clinical transplants.

DESIGN AND METHODS

We challenged C3H→AKR radiation chimeras with AKR-type splenocytes (i.e. recipient lymphocyte infusion) and BW5147.3 leukemia cells. We studied the kinetics of chimerism using flowcytometry and the mechanisms involved in antileukemic effects using in vivo antibody-mediated depletion of CD8(+) T and NK cells, and intracellular cytokine staining.

RESULTS

Whereas control chimeras showed progressive evolution towards high-level donor T-cell chimerism, recipient lymphocyte infusion chimeras showed a limited reduction of donor chimerism with delayed onset and long-term preservation of lower-level mixed chimerism. Recipient lymphocyte infusion chimeras nevertheless showed a significant survival benefit after leukemia challenge. In vivo antibody-mediated depletion experiments showed that both CD8(+) T cells and NK cells contribute to the antileukemic effect. Consistent with a role for NK cells, the proportion of IFN-γ producing NK cells in recipient lymphocyte infusion chimeras was significantly higher than in control chimeras.

CONCLUSIONS

In the MHC-matched setting, recipient lymphocyte infusion elicits lymphohematopoietic host-versus-graft reactivity that is limited but sufficient to provide an antileukemic effect, and this is dependent on CD8(+) T cells and NK cells. The data indicate that NK cells are activated as a bystander phenomenon during lymphohematopoietic T-cell alloreactivity and thus support a novel type of NK involvement in anti-tumor responses after post-transplant adoptive cell therapy.

A mechanistic rationale for combining alemtuzumab and rituximab in the treatment of ALL

B-lineage acute lymphoblastic leukemia (ALL) may express CD52 and CD20. Alemtuzumab (ALM) and rituximab (RTX) are therapeutic antibodies directed against CD52 and CD20, respectively, but showed limited activity against ALL in clinical trials. The mechanisms for the impaired responses remained unclear. We studied expression of CD52 and CD20 on ALL cells and found that most cases coexpressed CD52 and CD20. However, distinct CD52-negative (CD52(-)) subpopulations were detected in most cases as the result of defective glycophosphatidyl-inositol anchoring. Although ALM efficiently eradicated CD52-positive (CD52(+)) cells in NOD/scid mice engrafted with primary human ALL, CD52(-) subclones escaped therapy. In the same model, RTX showed limited activity resulting from occurrence of CD20 down-modulation. However, CD52(-) cells concurrently lacked the glycophosphatidyl-inositol-anchored complement regulators CD55 and CD59 and showed increased susceptibility to RTX-mediated complement-dependent cytotoxicity in vitro. At the same time, ALM was shown to inhibit down-modulation of CD20 in response to RTX by depleting the trogocytic capacity of phagocytic cells. Probably because of these complementary mechanisms, combined administration of ALM and RTX induced complete responses in vivo. Based on these data, we propose a mechanistic rationale for combined application of RTX and ALM in ALL.