HLA-haploidentical donor lymphocyte infusions for patients with relapsed hematologic malignancies after related HLA-haploidentical bone marrow transplantation

Specific Adoptive Cellular Immunotherapy in Allogeneic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) represents a treatment option for a diversity of advanced hematopoietic malignancies providing hope for long-term responses especially due to immunogenic effects associated with the treatment modality. Despite respectable progress in the field, relapses and/or opportunistic infections are major reasons for the high treatment-related mortality. However, a number of novel immunotherapeutic approaches using defined cell populations have been developed to directly target residual malignant cells as well as defined infectious diseases. We here provide an overview of current adoptive cellular immunotherapies in the context of allo-HSCT and close with an outlook on new directions within the field.

Donor-lymphocyte infusion following haploidentical hematopoietic cell transplantation with peripheral blood stem cell grafts and PTCy

Donor-lymphocyte infusion (DLI) for relapse following haploidentical hematopoietic cell transplantation (haploHCT) with post-transplant cyclophosphamide (PTCy) has been described in recipients of bone marrow grafts, but not recipients of G-CSF mobilized peripheral blood (PB) grafts. We retrospectively identified patients who underwent DLI following PB-haploHCT with PTCy for relapse, or loss of chimerism (LOC). Twelve patients (57%) received DLI for hematologic relapse/persistent disease, seven (33%) for extramedullary relapse and two (10%) for LOC. Sixteen (76%) received chemotherapy prior to DLI, which did not correlate with response. The most common first dose was 1 × 10⁶ CD3⁺ cells/kg. Two patients developed grade I aGvHD post DLI, one had grade II and two had grade III. One developed mild skin cGvHD 1361 days post DLI. Pre-DLI aGvHD predicted post-DLI aGvHD (P=0.025). Six patients achieved CR after DLI for overt relapse, one achieved full donor chimerism after LOC. Patients with LOC or EM relapse had superior relapse-free survival following DLI (P=0.029). DLI following PB-haploHCT with PTCy is a viable salvage therapy for overt relapse or LOC without a substantial increase in GvHD, and donor lymphocytes may be collected simultaneously with graft collection to facilitate availability in patients at high risk of relapse.

Optimizing peripheral blood stem cells transplantation outcome through amend relapse and graft failure: a review of current literature

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been considered as a valuable approach in treatment of numerous malignant and none malignant hematologic disorders. However, relapse and poor graft function (PGF) after allo-SCT remain to be controversial issues which may affect the transplantation outcome. Relevant articles were searched in MEDLINE database (2000–2016) using keywords and phrases: donor lymphocyte infusions, allogeneic stem cells transplantation, relapsed hematologic malignancies, booster schedules, cell dose, laboratory monitoring protocols and technical aspects of apheresis. Relapse of disease and PGF could be reduced via noting some main points such as choosing the suitable time and patient for donor lymphocyte infusion (DLI) and also determination of patients who ought to candidate for second allogeneic HSCT or for the use of stem cell boost. DLI and stem cell booster are promising treatment strategies noted in this review. Finally, this paper discusses indications and technical aspects of DLI and stem cell booster in hematological malignancies and emphasizes their therapeutic or pre-emptive potentials.

Major Histocompatibility Mismatch and Donor Choice for Second Allogeneic Bone Marrow Transplantation

Large alternative donor pools provide the potential for selecting a different donor for a second allogeneic (allo) bone or marrow transplant (BMT). As HLA disparity may contribute to the graft-versus-tumor effect, utilizing new mismatched haplotype donors may potentially improve the antitumor activity for relapsed hematologic malignancies despite a previous alloBMT. Data from patients who received a second alloBMT for relapsed hematologic malignancies at Johns Hopkins were analyzed. Outcomes were compared between patients who received a second allograft with the same MHC composition and those who received an allograft with a new mismatched haplotype. Loss of heterozygosity analysis was performed for patients with acute myeloid leukemia (AML) whose first allograft was haploidentical. Between 2005 and 2015, 40 patients received a second BMT for a relapsed hematologic malignancy. The median follow-up is 750 (range, 26 to 2950) days. The median overall survival (OS) in the cohort is 928 days (95% confidence interval [CI], 602 to not reached [NR]); median event-free survival (EFS) for the cohort is 500 days (95% CI, 355 to NR). The 4-year OS is 40% (95% CI, 25% to 64%), and the 4-year EFS is 36% (95% CI, 24% to 55%). The cumulative incidence of nonrelapsed mortality by 2 years was 27% (95% CI, 13% to 42%). The cumulative incidence of grade 3 to 4 acute graft-versus-host disease (GVHD) at 100 days was 15% (95% CI, 4% to 26%); the cumulative incidence of extensive chronic GVHD at 2 years was 22% (95% CI, 9% to 36%). The median survival was 552 days (95% CI, 376 to 2950+) in the group who underwent transplantation with a second allograft that did not harbor a new mismatched haplotype, while it was not reached in the group whose allograft contained a new mismatched haplotype (hazard ratio [HR], .36; 95% CI, .14 to .9; P = .02). EFS was also longer in the group who received an allograft containing a new mismatched haplotype, (NR versus 401 days; HR, .50; 95% CI, .22 to 1.14; P = .09). Although the allograft for this patient's second BMT contained a new mismatched haplotype, AML nevertheless relapsed a second time. Second BMTs are feasible and provide a reasonable chance of long-term survival. An allograft with a new mismatched haplotype may improve outcomes after second BMTs for relapsed hematologic malignancies.

Outcomes of haploidentical transplant compared with matched donor allogeneic stem cell transplant

The risk of acute and chronic graft-versus-host disease (GVHD) with haploidentical transplant with post-transplant high-dose cyclophosphamide may be lower compared with matched unrelated donor transplant and largely similar to matched related donor transplant. The lower probability of GVHD with the haploidentical donor may result in a risk of nonrelapse mortality that is at least similar to or even lower than the matched donor. The incidence of relapse and survival are also largely similar to different donor types. Haploidentical transplant may be associated with slower engraftment. Given a lower risk of GVHD, haploidentical transplant has gained popularity. Additionally, the use of post-transplant high-dose cyclophosphamide has been extended to lower the risk of GVHD with matched donor and mismatched unrelated donor transplant.

Nonmyeloablative Haploidentical Bone Marrow Transplantation with Post-Transplantation Cyclophosphamide for Pediatric and Young Adult Patients with High-Risk Hematologic Malignancies

Lower-intensity conditioning regimens for haploidentical blood or marrow transplantation (BMT) are safe and efficacious for adult patients with hematologic malignancies. We report data for pediatric/young adult patients with high-risk hematologic malignancies (n = 40) treated with nonmyeloablative haploidentical BMT with post-transplantation cyclophosphamide from 2003 to 2015. Patients received a preparative regimen of fludarabine, cyclophosphamide, and total body irradiation. Post-transplantation immunosuppression consisted of cyclophosphamide, mycophenolate mofetil, and tacrolimus. Donor engraftment occurred in 29 of 32 (91%), with median time to engraftment of neutrophils >500/µL of 16 days (range, 13 to 22) and for platelets >20,000/µL without transfusion of 18 days (range, 12 to 62). Cumulative incidences of acute graft-versus-host disease (GVHD) grades II to IV and grades III and IV at day 100 were 33% and 5%, respectively. The cumulative incidence of chronic GVHD was 23%, with 7% moderate-to-severe chronic GVHD, according to National Institutes of Health consensus criteria. Transplantation-related mortality (TRM) at 1 year was 13%. The cumulative incidence of relapse at 2 years was 52%. With a median follow-up of 20 months (range, 3 to 148), 1-year actuarial overall and event-free survival were 56% and 43%, respectively. Thus, we demonstrate excellent rates of engraftment, GVHD, and TRM in pediatric/young adult patients treated with this regimen. This approach is a widely available, safe, and feasible option for pediatric and young adult patients with high-risk hematologic malignancies, including those with a prior history of myeloablative BMT and/or those with comorbidities or organ dysfunction that preclude eligibility for myeloablative BMT.

T Cell-Replete Peripheral Blood Haploidentical Hematopoietic Cell Transplantation with Post-Transplantation Cyclophosphamide Results in Outcomes Similar to Transplantation from Traditionally Matched Donors in Active Disease Acute Myeloid Leukemia

Outcomes for patients with acute myeloid leukemia (AML) who fail to achieve complete remission remain poor. Hematopoietic cell transplantation (HCT) has been shown to induce long-term survival in AML patients with active disease. HCT is largely performed with HLA-matched unrelated or HLA-matched related donors. Recently, HCT with HLA-haploidentical related donors has been identified as a feasible option when HLA-matched donors are not immediately available. However, there are little data comparing outcomes for AML patients with active disease who receive haploidentical versus traditionally matched HCT. We retrospectively analyzed data from 99 AML patients with active disease undergoing allogeneic HCT at a single institution. Forty-three patients received unrelated donor HCT, 32 patients received matched related donor HCT, and 24 patients received peripheral blood haploidentical HCT with post-transplantation cyclophosphamide. We found no significant differences between treatment groups in terms of overall survival (OS), event-free survival, transplantation-related mortality, cumulative incidence of relapse, and cumulative incidence of acute and chronic graft-versus-host disease (GVHD). We performed univariate regression analysis of variables that modified OS in all patients and found only younger age at transplantation and development of chronic GVHD significantly improved outcome. Although limited by our relatively small sample size, these results indicate that haploidentical HCT in active AML patients have comparable outcomes to HCT with traditionally matched donors. Haploidentical HCT can be considered in this population of high-risk patients when matched donors are unavailable or when wait times for transplantation are unacceptably long.

Comparable composite endpoints after HLA-matched and HLA-haploidentical transplantation with post-transplantation cyclophosphamide

Composite endpoints that not only encompass mortality and relapse, but other critical post-transplant events such as graft-versus-host disease, are being increasingly utilized to quantify survival without significant morbidity after allogeneic blood or marrow transplantation. High-dose, post-transplantation cyclophosphamide reduces severe graft-versus-host disease with allogeneic marrow transplantation, making composite endpoints after this management particularly interesting. We retrospectively analyzed 684 adults with hematologic malignancies who received T-cell-replete bone marrow grafts and cyclophosphamide after myeloablative HLA-matched related (n=192) or unrelated (n=120), or non-myeloablative HLA-haploidentical (n=372) donor transplantation. The median follow up was 4 (range, 0.02-11.4) years. Graft-versus-host disease-free, relapse-free survival was defined as the time after transplantation without grade III-IV acute graft-versus-host disease, chronic graft-versus-host disease requiring systemic treatment, relapse, or death. Chronic graft-versus-host disease-free, relapse-free survival was defined as the time after transplantation without moderate or severe chronic graft-versus-host disease, relapse, or death. One-year graft-versus-host disease-free, relapse-free survival and chronic graft-versus-host disease-free, relapse-free survival estimates were, respectively, 47% (95% CI: 41-55%) and 53% (95% CI: 46-61%) after myeloablative HLA-matched related, 42% (95% CI: 34-52%) and 52% (95% CI: 44-62%) after myeloablative HLA-matched unrelated, and 45% (95% CI: 40-50%) and 50% (95% CI: 45-55%) after non-myeloablative HLA-haploidentical donor transplantation. In multivariable models, there were no differences in graft-versus-host disease-free, or chronic graft-versus-host disease-free, relapse-free survival after either myeloablative HLA-matched unrelated or non-myeloablative HLA-haploidentical, compared with myeloablative HLA-matched related donor transplantation. Although limited by inclusion of dissimilar cohorts, we found that post-transplantation cyclophosphamide-based platforms yield comparable composite endpoints across conditioning intensity, donor type, and HLA match.

Persistent Multiyear Control of Relapsed T-Cell Acute Lymphoblastic Leukemia With Successive Donor Lymphocyte Infusions: A Case Report

There are few therapeutic options for patients with T-cell acute lymphoblastic leukemia (T-ALL) who have recurrent disease after initial matched sibling hematopoietic stem cell transplantation. While a second hematopoietic stem cell transplant (HSCT) from a haploidentical donor offers the conceptual possibility of greater graft versus leukemia effect, there is minimal literature to describe the efficacy of this approach in recurrent pediatric T-ALL. We present the case of a now 9-year-old female in whom second haploidentical HSCT, followed by successive donor lymphocyte infusions in response to minimal residual disease reemergence, has led to 3+ years of ongoing disease control without graft versus host disease and excellent quality of life.

Donor lymphocyte infusion after allogeneic stem cell transplantation

Allogeneic stem cell transplantation (allo-SCT) is considered the cornerstone in the treatment of several malignant and not malignant hematological diseases. However, relapse of hematological disease after allo-SCT is considered the most challenging point in the field. The risk can be reduced through optimal patients, donor and disease selection before allo-SCT, but harnessing donor immune system is an appealing way to treat or avoid disease relapse. Donor lymphocyte infusion (DLI) is a simple and effective therapy after allo-SCT. In this paper, the efficacy of DLI will be analyzed in different hematological diseases, focusing also on their therapeutic or pre-emptive use.

Post-relapse survival after haploidentical transplantation vs matched-related or matched-unrelated hematopoietic cell transplantation

Relapse remains a major cause of mortality among patients receiving allogeneic hematopoietic cell transplantation (HCT). The impact of donor type on post-relapse survival (PRS) has not been widely examined. We compared the survival outcomes for patients relapsing after haploidentical donor transplantation (HIDT) using post-transplant cyclophosphamide with those relapsing after matched-related donor transplantation (MRDT) or matched-unrelated donor transplantation (MUDT) at our institution. Two hundred and thirty-seven consecutive HCT recipients with relapse occurring after HIDT (N=48), MUDT (N=87) and MRDT (N=102) were included in this analysis. Median age was 49 years (19-77 years) and the median time to relapse was 156 days (12-2465) after HCT. HIDT recipients had similar median time to relapse (5.8 vs 4.8 vs 5.5 months, P=0.638) compared with MUDT and MRDT, respectively. One-year PRS was worse among HIDT recipients compared with MRDT and MUDT (17% vs 46% vs 40%, P<0.05). In a multivariate analysis, time to relapse (<3 vs >3 months post transplant), no use of donor lymphocyte infusion (DLI) following relapse, higher Dana Farber disease risk index and HCT comorbidity index scores at the time of transplant and delayed platelet engraftment post transplant were all predictive of worse PRS. This analysis shows that 1-year PRS is inferior among HIDT when compared with MRDT or MUDT. Lower use of DLI after HIDT may have contributed to this inferior survival.

Haploidentical, G-CSF-primed, unmanipulated bone marrow transplantation for patients with high-risk hematological malignancies: an update

Ninety-seven patients affected by high-risk hematological malignancies underwent G-CSF primed, unmanipulated bone marrow (BM) transplantation from a related, haploidentical donor. All patients were prepared with an identical conditioning regimen including Thiotepa, Busilvex, Fludarabine (TBF) and antithymocyte globulin given at myeloablative (MAC = 68) or reduced (reduced intensity conditioning (RIC) = 29) dose intensity and received the same GvHD prophylaxis consisting of the combination of methotrexate, cyclosporine, mycofenolate-mofetil and basiliximab. Patients were transplanted in 1st or 2nd CR (early phase: n = 60) or in > 2nd CR or active disease (advanced phase: n = 37). With a median time of 21 days (range 12-38 days), the cumulative incidence (CI) of neutrophil engraftment was 94 ± 3%. The 100-day CI of III-IV grade acute GvHD and the 2-year CI of extensive chronic GvHD were 9 ± 3% and 12 ± 4%, respectively. Overall, at a median follow-up of 2.2 years (range 0.3-5.6), 44 out of 97 (45%) patients are alive in CR. The 5-year probability of overall survival (OS) and disease-free survival (DFS) for patients in early and advanced phase was 53 ± 7 vs 24 ± 8% (P = 0.006) and 48 ± 7 vs 22 ± 8% (P = 0.01), respectively. By comparing MAC with RIC patient groups, the transplant-related mortality was equivalent (36 ± 6 vs 28 ± 9%) while the relapse risk was lower for the MAC patients (22 ± 6 vs 45 ± 11%), who showed higher OS (48 ± 7 vs 29 ± 10%) and DFS (43 ± 7 vs 26 ± 10%). However, all these differences did not reach a statistical significance. In multivariate analysis, diagnosis and recipient age were significant factors for OS and DFS. In conclusion, this analysis confirms, on a longer follow-up and higher number of patients, our previous encouraging results obtained by using MAC and RIC TBF regimen as conditioning for G-CSF primed, unmanipulated BM transplantation from related, haploidentical donor in patients with high-risk hematological malignancies, lacking an HLA-identical sibling or unrelated donor and in need to be urgently transplanted.

Strategies for improving the efficacy of donor lymphocyte infusion following stem cell transplantation

Donor lymphocyte infusion (DLI) is an effective immunotherapeutic approach with significant activity in the treatment and prevention of relapse after allogeneic stem cell transplantation. DLI is associated with significant toxicity mainly due to graft-versus-host disease. Moreover, DLI does not produce durable responses in aggressive malignancies like acute leukemia. Improvement in DLI efficacy requires dissociation of graft-versus-leukemia effect from graft-versus-host disease. Minor histocompatibility antigens with tissue restriction and leukemia or tumor-associated antigens represent ideal antigenic targets. A brief overview of the existing methods of DLI administration is the topic of this article. T cells transduced with genes encoding for T-cell receptors with reactivity against minor histocompatibility antigens or leukemia-associated antigens is a promising option.

New strategies of DLI in the management of relapse of hematological malignancies after allogeneic hematopoietic SCT

DLI is an effective strategy for patients with recurrent hematological malignancies after allogeneic hematopoietic SCT (allo-HSCT). DLI has been widely applied to boost the graft vs tumor (GVT) or GVL effects. However, given the potentially severe complications associated with conventional DLI and transient GVL effect, new strategies for DLI are emerging. In this review, we have discussed the recent important studies on DLI as a prophylactic or therapeutic modality for relapsed hematological disorders after allo-HSCT. The strategies to separate GVL from GVHD have also been discussed. Leukemia-targeting therapy and lymphodepletion combined with DLI, and prophylactic DLI after allo-HSCT are often employed for patients with high risk of relapse, which has been reviewed as well. In addition, we have also discussed the issues on DLI to be further addressed, such as the doses, timing and frequency of DLI in different clinical settings, leukemic antigen-specific DLI as well as how to augment GVL effect while attenuating GVHD.

Outcomes of Nonmyeloablative HLA-Haploidentical Blood or Marrow Transplantation With High-Dose Post-Transplantation Cyclophosphamide in Older Adults

PURPOSE

Recent advances in nonmyeloablative (NMA), related HLA-haploidentical blood or marrow transplantation (haplo-BMT) have expanded the donor pool. This study evaluated the effect of age on NMA haplo-BMT outcomes in patients age 50 to 75 years.

PATIENTS AND METHODS

A retrospective analysis was performed of 271 consecutive patients with hematologic malignancies, age 50 to 75 years, who received NMA, T-cell-replete haplo-BMT with high-dose post-transplantation cyclophosphamide.

RESULTS

The median age was 61 years, with 115 patients (42%) age 50 to 59, 129 (48%) age 60 to 69, and 27 (10%) age 70 to 75 years. Overall, 84% of patients had intermediate- or high-/very high-risk disease. The 6-month probabilities of grade 3 or 4 acute graft-versus-host disease (GVHD) and nonrelapse mortality (NRM) were 3% and 8%, respectively. Patients in their 50s, 60s, and 70s had 6-month NRM probabilities of 8%, 9%, and 7%, respectively (P=.20). With a median follow-up of 4 years, corresponding 3-year progression-free survival probabilities were 39%, 35%, and 33% (P=.65), and corresponding 3-year overall survival probabilities were 48%, 45%, and 44% (P=.66). Three-year progression-free survival probabilities were 40% in acute myeloid leukemia (n=65), 39% in aggressive non-Hodgkin lymphoma (n=83), and 37% in indolent or mantle-cell lymphoma (n=65). Older patient age was associated with a significantly higher risk of grade 2 to 4 acute GVHD but not grade 3 to 4 acute or chronic GVHD. No statistically significant associations were found between older age (relative to age 50 to 59 years or as a continuous variable) and NRM, relapse, or survival.

CONCLUSION

NMA haplo-BMT with post-transplantation cyclophosphamide has encouraging safety and survival outcomes in patients age 50 to 75 years. In patients otherwise fit for BMT, the results support consideration of this approach despite advanced age.

Haploidentical Hematopoietic Stem Cell Transplantation as a Platform for Post-Transplantation Cellular Therapy

Haploidentical transplantation can extend the opportunity for transplantation to almost all patients who lack an HLA-matched donor. Advances in the field of haploidentical transplantation have led to a marked decrease in treatment-related mortality, allowing investigators to focus on developing rationale pre- and peri-remission therapies aimed at preventing disease relapse after transplantation. Because of widespread availability, low treatment-related mortality, and cost, haploidentical donors may become the preferred "alternative" donors for allogeneic hematopoietic stem cell transplantation. One of the major advantages of using a related donor is the possibility of collecting or generating additional cellular products from the same immediately available donor, which will not be rejected. Infusion of these cells in the peri-transplantation period, derived from the same immune system, is opening the possibility of markedly enhancing the antitumor effects of the graft and hastening immunologic reconstitution after transplantation.

"No donor"? Consider a haploidentical transplant

Haploidentical stem cell transplantation (HaploSCT) is an attractive option for patients requiring a hematopoietic stem cell transplant who do not have an HLA-matched donor, because it is cheaper, can be performed faster, and may extend transplantation to virtually all patients in need. Significant advances have been made in the recent decade with dramatic improvement in treatment outcomes. Historically, overcoming the HLA-incompatibility barrier has been a significant limitation to the expansion of this form of transplant. While ex vivo T-cell depletion effectively prevented the development of acute GVHD, it was associated with a higher treatment-related mortality, in excess of 40% in some series, due to a significant delay in recovery of the adaptive immune system. Newer methods have successfully maintained the memory T cells in the graft and/or selectively depleted alloreactive T cells, and are associated with improved treatment outcomes. Post-transplant cyclophosphamide for GVHD prevention has proven very effective in controlling GVHD with lower incidence of infectious complications and treatment-related mortality-as low as 7% at 1 year-and has become the new standard in how this transplant is performed. Here, we reviewed the current experience with this approach and various other strategies employed to control alloreactivity in this setting, including selective depletion of T cells from the graft, as well as we discuss post-transplantation therapy to prevent disease relapse and improve immunologic reconstitution.

Sequential therapy combining clofarabine and T-cell-replete HLA-haploidentical haematopoietic SCT is feasible and shows efficacy in the treatment of refractory or relapsed aggressive lymphoma

Prognosis is poor for patients with biologically aggressive Non-Hodgkin lymphoma (NHL), refractory to chemotherapy or relapsed after autologous transplantation, especially when no disease control before allogeneic transplantation is achieved. In 16 patients (median age 53, median prior regimes 5) with relapsed or refractory non-remission NHL, we analysed retrospectively the efficacy of a sequential therapy comprising clofarabine re-induction followed by a reduced-intensity conditioning with fludarabine, CY and melphalan, and T-cell-replete HLA-haploidentical transplantation. High-dose CY was utilized post-transplantation. All patients engrafted. Early response (day +30) was achieved in 94%. Treatment-related grade III-IV toxicity occurred in 56%, most commonly transient elevation of transaminases (36%), while there was a low incidence of infections (19% CMV reactivation, 19% invasive fungal infection) and GVHD (GVHD: acute III-IV: 6%; mild chronic: 25%). One-year non-relapse mortality was 19%. After a median follow-up of 21 months, estimated 1- and 2-year PFS was 56 and 50%, respectively, with 11 patients (69%) still alive after 2 years. In summary, sequential therapy is feasible and effective and provides an acceptable toxicity profile in high-risk non-remission NHL. Presumably, cytotoxic reinduction with clofarabine provides enough remission time for the graft-versus lymphoma effect of HLA-haploidentical transplantation to kick in, even in lymphomas that are otherwise chemo-refractory.

Strategies for the identification of T cell-recognized tumor antigens in hematological malignancies for improved graft-versus-tumor responses after allogeneic blood and marrow transplantation

Allogeneic blood and marrow transplantation (allo-BMT) is an effective immunotherapeutic treatment that can provide partial or complete remission for patients with hematological malignancies. Mature donor T cells in the donor inoculum play a central role in mediating graft-versus-tumor (GVT) responses by destroying residual tumor cells that persist after conditioning regimens. Alloreactivity towards minor histocompatibility antigens (miHA), which are varied tissue-related self-peptides presented in the context of major histocompatibility complex (MHC) molecules on recipient cells, some of which may be shared on tumor cells, is a dominant factor for the development of GVT. Potentially, GVT can also be directed to tumor-associated antigens or tumor-specific antigens that are more specific to the tumor cells themselves. The full exploitation of allo-BMT, however, is greatly limited by the development of graft-versus-host disease (GVHD), which is mediated by the donor T cell response against the miHA expressed in the recipient's cells of the intestine, skin, and liver. Because of the significance of GVT and GVHD responses in determining the clinical outcome of patients, miHA and tumor antigens have been intensively studied, and one active immunotherapeutic approach to separate these two responses has been cancer vaccination after allo-BMT. The combination of these two strategies has an advantage over vaccination of the patient without allo-BMT because his or her immune system has already been exposed and rendered unresponsive to the tumor antigens. The conditioning for allo-BMT eliminates the patient's existing immune system, including regulatory elements, and provides a more permissive environment for the newly developing donor immune compartment to selectively target the malignant cells. Utilizing recent technological advances, the identities of many human miHA and tumor antigenic peptides have been defined and are currently being evaluated in clinical and basic immunological studies for their ability to produce effective T cell responses. The first step towards this goal is the identification of targetable tumor antigens. In this review, we will highlight some of the technologies currently used to identify tumor antigens and anti-tumor T cell clones in hematological malignancies.