Susceptibility of malignant plasma cells to HA-1H specific lysis suggests a role for the minor histocompatibility antigen HA-1 in the graft-versus-myeloma effect

Allogeneic Hematopoietic Cell Transplantation for Myeloma: When and in Whom Does It Work

The growing list of available therapies for patients with multiple myeloma has resulted in tremendously high response rates and prolonged survival. However, the cure remains elusive. A continued effort at developing strategies to utilize all available treatment modalities in the most effective manner is needed. Allogeneic hematopoietic cell transplantation (allo-HCT) is a robust platform, associated with high response rates, and provides a unique foundation on which immune therapies and novel agents can be employed to improve clinical outcomes. Patients with high-risk myeloma and those relapsing after novel agent-based therapies or early after an autologous HCT should be considered for allo-HCT, ideally in a clinical trial setting. Results from several ongoing studies are expected to provide important information that will help determine the place of allo-HCT in the myeloma treatment algorithm.

Hematopoietic stem cell-derived myeloid and plasmacytoid DC-based vaccines are highly potent inducers of tumor-reactive T cell and NK cell responses ex vivo

Because of the potent graft-versus-tumor (GVT) effect, allogeneic stem cell transplantation (alloSCT) can be a curative therapy for hematological malignancies. However, relapse remains the most frequent cause of treatment failure, illustrating the necessity for development of adjuvant post-transplant therapies to boost GVT immunity. Dendritic cell (DC) vaccination is a promising strategy in this respect, in particular, where distinct biologic functions of naturally occurring DC subsets, i.e. myeloid DCs (mDCs) and plasmacytoid DCs (pDCs), are harnessed. However, it is challenging to obtain high enough numbers of primary DC subsets from blood for immunotherapy due to their low frequencies. Therefore, we present here an ex vivo GMP-compliant cell culture protocol for generating different DC subsets from CD34⁺ hematopoietic stem and progenitor cells (HSPCs) of alloSCT donor origin. High numbers of BDCA1⁺ mDCs and pDCs could be generated, sufficient for multiple vaccination cycles. These HSPC-derived DC subsets were highly potent in inducing antitumor immune responses in vitro. Notably, HSPC-derived BDCA1⁺ mDCs were superior in eliciting T cell responses. They efficiently primed naïve T cells and robustly expanded patient-derived minor histocompatibility antigen (MiHA)-specific T cells. Though the HSPC-pDCs also efficiently induced T cell responses, they exhibited superior capacity in activating NK cells. pDC-primed NK cells highly upregulated TRAIL and possessed strong cytolytic capacity against tumor cells. Collectively, these findings indicate that HSPC-derived DC vaccines, comprising both mDCs and pDCs, may possess superior potential to boost antitumor immunity post alloSCT, due to their exceptional T cell and NK cell stimulatory capacity.

Possible role of minor h antigens in the persistence of donor chimerism after stem cell transplantation; relevance for sustained leukemia remission

Persistent complete donor chimerism is an important clinical indicator for remissions of hematological malignancies after HLA-matched allogeneic stem cell transplantation (SCT). However, the mechanisms mediating the persistence of complete donor chimerism are poorly understood. The frequent coincidence of complete donor chimerism with graft-versus-leukemia effects and graft-versus-host disease suggests that immune responses against minor histocompatibility antigens (mHags) are playing an important role in suppressing the host hematopoiesis after allogeneic SCT. Here, we investigated a possible relationship between donor immune responses against the hematopoiesis-restricted mHag HA-1 and the long-term kinetics of host hematopoietic chimerism in a cohort of 10 patients after allogeneic HLA-matched, HA-1 mismatched SCT. Functional HA-1 specific CTLs (HA-1 CTLs) were detectable in 6/10 patients lysing host-type hematopoietic cells in vitro. Presence of HA-1 CTLs in the peripheral blood coincided with low host hematopoiesis levels quantified by highly sensitive mHag specific PCR. Additionally, co-incubation of host type CD34⁺ cells with HA-1 CTLs isolated after allogeneic SCT prevented progenitor and cobblestone area forming cell growth in vitro and human hematopoietic engraftment in immunodeficient mice. Conversely, absence or loss of HA-1 CTLs mostly coincided with high host hematopoiesis levels and/or relapse. In summary, in this first study, presence of HA-1 CTLs paralleled low host hematopoiesis levels. This coincidence might be supported by the capacity of HA-1 CTLs isolated after allogeneic SCT to specifically eliminate host type hematopoietic stem/progenitor cells. Additional studies involving multiple mismatched mHags in more patients are required to confirm this novel characteristic of mHag CTLs as factor for the persistence of complete donor chimerism and leukemia remission after allogeneic SCT.

Targeting multiple-myeloma-induced immune dysfunction to improve immunotherapy outcomes

Multiple myeloma (MM) is a plasma cell malignancy associated with high levels of monoclonal (M) protein in the blood and/or serum. MM can occur de novo or evolve from benign monoclonal gammopathy of undetermined significance (MGUS). Current translational research into MM focuses on the development of combination therapies directed against molecularly defined targets and that are aimed at achieving durable clinical responses. MM cells have a unique ability to evade immunosurveillance through several mechanisms including, among others, expansion of regulatory T cells (Treg), reduced T-cell cytotoxic activity and responsiveness to IL-2, defects in B-cell immunity, and induction of dendritic cell (DC) dysfunction. Immune defects could be a major cause of failure of the recent immunotherapy trials in MM. This article summarizes our current knowledge on the molecular determinants of immune evasion in patients with MM and highlights how these pathways can be targeted to improve patients' clinical outcome.

International Myeloma Working Group Consensus Statement Regarding the Current Status of Allogeneic Stem-Cell Transplantation for Multiple Myeloma

Purpose

To define consensus statement regarding allogeneic stem-cell transplantation (Allo-SCT) as a treatment option for multiple myeloma (MM) on behalf of International Myeloma Working Group.

Patients and Methods

In this review, results from prospective and retrospective studies of Allo-SCT in MM are summarized.

Results

Although the introduction of reduced-intensity conditioning (RIC) has lowered the high treatment-related mortality associated with myeloablative conditioning, convincing evidence is lacking that Allo-RIC improves the survival compared with autologous stem-cell transplantation.

Conclusion

New strategies are necessary to make Allo-SCT safer and more effective for patients with MM. Until this is achieved, Allo-RIC in myeloma should only be recommended in the context of clinical trials.

Correlation of high-resolution X-ray micro-computed tomography with bioluminescence imaging of multiple myeloma growth in a xenograft mouse model

Multiple myeloma (MM) is an incurable B-cell neoplasia in which progressive skeletal lesions are a characteristic feature. Earlier we established an animal model for human MM in the immune-deficient RAG2(-/-)gammac(-/-) mouse, in which the growth of luciferase-transduced MM cells was visualized using noninvasive bioluminescence imaging (BLI). This model appeared well suited to study disease progression and response to therapy by identifying the location of various foci of MM tumor growth scattered throughout the skeleton and at subsequent time points the quantitative assessment of the tumor load by using BLI. We report here on the corresponding high-resolution X-ray micro-computed tomographic (micro-CT) analysis to study skeletal defects in the mice with full-blown MM. Several anatomical derangements were observed, including abnormalities in geometry and morphology, asymmetrical bone structures, decreased overall density in the remaining bone, loss of trabecular bone mass, destruction of the inner microarchitecture, as well as cortical perforations. Using the combination of BLI, micro-CT imaging, and immune-histopathological techniques, we found a high correlation between the micro-CT-identified lesions, exact tumor location, and infiltration leading to structural lesions and local bone deformation. This confirms that this animal model strongly resembles human MM and has the potential for studying the biology of MM growth and for preclinical testing of novel therapies for MM and for repair of MM-induced bone lesions.

Partial T cell-depleted allogeneic stem cell transplantation following reduced-intensity conditioning creates a platform for immunotherapy with donor lymphocyte infusion and recipient dendritic cell vaccination in multiple myeloma

Allogeneic stem cell transplantation (SCT) in multiple myeloma (MM) may induce a curative graft-versus-myeloma (GVM) effect. Major drawback in unmanipulated reduced-intensity conditioning (RIC) SCT is the risk of severe and longstanding graft-versus-host-disease (GVHD). This study demonstrates that transplantation with a partial T cell-depleted graft creates a platform for boosting GVM immunity by preemptive donor lymphocyte infusion (DLI) and recipient dendritic cell (DC) vaccination, with limited GVHD. All 20MM patients engrafted successfully. Chimerism analysis in 19 patients evaluable at 3 months revealed that 7 patients were complete donor, whereas 12 patients were mixed chimeric. Grade II acute GVHD (aGVHD) occurred in 7 patients (35%) and only 4 patients (21%) developed chronic GVHD (cGVHD). Fourteen patients received posttransplantation immunotherapy, 8 preemptive DLI, 5 patients both DLI and DC vaccination, and 1 patient DC vaccination only. DC vaccination was associated with limited toxicity, and none of these patients developed GVHD. Importantly, overall treatment-related mortality (TRM) at 1 year was low (10%). Moreover, the overall survival (OS) is 84% with median follow-up of 27 months, and none of the patients died from progressive disease. These findings illustrate that this novel approach is associated with limited GVHD and mortality, thus creating an ideal platform for adjuvant immunotherapy.

Rebuilding Human Leukocyte Antigen Class II–Restricted Minor Histocompatibility Antigen Specificity in Recall Antigen-Specific T Cells by Adoptive T Cell Receptor Transfer: Implications for Adoptive Immunotherapy

PURPOSE

Donor T cells directed to hematopoietic minor histocompatibility antigens (mHag) are appealing tools for adoptive immunotherapy of hematological malignancies after allogeneic stem cell transplantation (allo-SCT). Toward the development of a convenient strategy for ex vivo generation of human leukocyte antigen (HLA) class II--restricted mHag-specific T cells, we evaluated the feasibility of rebuilding mHag-specific T cell functions in donor-derived recall antigen-specific T cells via T cell receptor (TCR) transfer.

EXPERIMENTAL DESIGN

TCR alpha- and beta-chains of an HLA-DPB1*0401--restricted T-cell clone recognizing a multiple myeloma-associated mHag were retrovirally transferred into a tetanus toxoid (TT)--specific clone derived from the original stem cell donor. TCR double-transduced cells were compared with the parent mHag- and TT-specific clones for antigen specificity, cytokine secretion, and cytotoxic activity and were analyzed for their in vitro expansion capacity in a TT- or mHag-specific fashion.

RESULTS

mHag-TCR--transduced TT-specific cells displayed both TT and mHag specificity. Similar to the parent cells, they secreted Th-1 cytokines and exerted significant cytotoxic activity against TT-pulsed or mHag(+) target cells, including multiple myeloma cells. A 4-week expansion of TCR-transduced cells via the TT-specific TCR had no negative influence on the mHag-specific cytotoxic activity and resulted in 10- to 100-fold better cell yields as compared with mHag-specific expansion.

CONCLUSIONS

HLA class II--restricted, mHag-specific effector functions can be successfully reconstructed in donor-derived TT-specific T cells via TCR transfer. Effective expansion of these T cells via TT-specific TCRs illustrate the suitability of this strategy for ex vivo expansion and possibly for in vivo TT-specific reboosting of HLA class II--restricted immunotherapeutic T cells.

DNA fusion vaccines induce epitope-specific cytotoxic CD8(+) T cells against human leukemia-associated minor histocompatibility antigens

The graft-versus-leukemia effect of allogeneic stem-cell transplantation is believed to be mediated by T-cell recognition of minor histocompatibility antigens on recipient cells. For minor histocompatibility antigens HA-1 and HA-2, normal cell expression is restricted to hemopoietic cells, and boosting the immune response to these antigens may potentiate graft-versus-leukemia effect without accompanying graft-versus-host disease. To increase efficacy, expansion of HA-1- or HA-2-specific CTL before transplantation is desirable. However, primary HA-1- or HA-2-specific CTL expanded in vitro are often of low avidity. An alternative approach is to prime specific CTL responses in vivo by vaccination. Clearly, donor vaccination must be safe and specific. We have developed DNA fusion vaccines able to induce high levels of epitope-specific CTL using linked CD4(+) T-cell help. The vaccines incorporate a domain of tetanus toxin (DOM) fused to a sequence encoding a candidate MHC class I binding peptide. This design generates antitumor CD8(+) T-cell responses and protective immunity in preclinical models. For clinical application, we constructed vaccines encoding HLA-A*0201-restricted peptides from human HA-1 and HA-2, which were fused to DOM, and tested their performance in HLA-A*0201-transgenic mice. Priming induced epitope-specific, IFNgamma-producing CD8(+) T cells with cytotoxic function boosted to high levels with electroporation. Strikingly, these mouse T cells efficiently killed human lymphoblastoid cell lines expressing endogenous HA-1 or HA-2. High avidity is indicated by the independence of cytolysis from CD8/MHC class I interaction. These safe epitope-specific vaccines offer a potential strategy to prime HA-1- or HA-2-specific CTL in transplant donors before adoptive transfer.