Induction of alloantigen-specific anergy in human peripheral blood mononuclear cells by alloantigen stimulation with co-stimulatory signal blockade

The graft versus leukemia effect: donor lymphocyte infusions and cellular therapy

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative therapy for many hematologic malignancies as well as non-malignant conditions. Part of the curative basis underlying HSCT for hematologic malignancies relies upon induction of the graft versus leukemia (GVL) effect in which donor immune cells recognize and eliminate residual malignant cells within the recipient, thereby maintaining remission. GVL is a clinically evident phenomenon; however, specific cell types responsible for inducing this effect and molecular mechanisms involved remain largely undefined. One of the best examples of GVL is observed after donor lymphocyte infusions (DLI), an established therapy for relapsed disease or incipient/anticipated relapse. DLI involves infusion of peripheral blood lymphocytes from the original HSCT donor into the recipient. Sustained remission can be observed in 20-80% of patients treated with DLI depending upon the underlying disease and the intrinsic burden of targeted cells. In this review, we will discuss current knowledge about mechanisms of GVL after DLI, experimental strategies for augmenting GVL by manipulation of DLI (e.g. neoantigen vaccination, specific cell type selection/depletion) and research outlook for improving DLI and cellular immunotherapies for hematologic malignancies through better molecular definition of the GVL effect.

Prophylactic donor lymphocyte infusion for relapse prevention: a meta-analysis

OBJECTIVE

Primary disease relapse (PDR) of malignant hematologic conditions after standard hematopoietic stem cell transplant (HSCT) is one of the most challenging diseases; therefore ongoing researches are aiming at relapse prevention and minimizing the transplant-related side effects. Prophylactic donor lymphocytes (pDLI) had been proposed as a valuable strategy for PDR prevention, but early studies had been discouraging due to the limited benefit and possible association with acute graft-versus-host disease (aGVHD). Therefore, we conducted a meta-analysis to evaluate the association between pDLI use, PDR, aGVHD and OS.

METHOD

We performed a comprehensive literature search in MEDLINE, Cochrane library and Embase database from inception to May 2019 for studies that evaluated the association between pDLI and PDR. We conducted a random effect meta-analysis of 9 studies involving a total of 748 participants (pDLI = 398, non-pDLI = 350) and reported the pooled odd ratio (OR) for association of pDLI use, PDR, aGVHD and OS.

RESULT

We found a significant decreased odd of PDR in the pDLI group (pooled OR = 0.42, 95% CI 0.30-0.58, I2 = 0%), but there was no significant increased odd of aGVHD (pooled OR of 0.98, 95% CI 0.56-1.72, I2 = 0.8%). We also found that there was an increased odd of overall survival (OS) (pooled OR 3.17, 95% CI 1.85-5.45, I2 = 50.2%).

CONCLUSION

There are significantly decreased odd of PDR and increased odd of OS in the pDLI group compared to the control group, but there is no statistically significant increased odd of aGVHD as suggested by previous studies. We concluded that pDLI is a potentially valuable method for post-transplant PDR prevention.

Virus-Specific T Cells for the Immunocompromised Patient

While progress has been made in the treatment of both hematologic cancers and solid tumors, chemorefractory or relapsed disease often portends a dismal prognosis, and salvage chemotherapy or radiation expose patients to intolerable toxicities and may not be effective. Hematopoietic stem cell transplant offers the promise of cure for many patients, and while mismatched, unrelated or haploidentical donors are increasingly available, the recipients are at higher risk of severe immunosuppression and immune dysregulation due to graft versus host disease. Viral infections remain a primary cause of severe morbidity and mortality in this patient population. Again, many therapeutic options for viral disease are toxic, may be ineffective or generate resistance, or fail to convey long-term protection. Adoptive cell therapy with virus-specific T cells (VSTs) is a targeted therapy that is efficacious and has minimal toxicity in immunocompromised patients with CMV and EBV infections in particular. Products have since been generated specific for multiple viral antigens (multi-VST), which are not only effective but also confer protection in 70–90% of recipients when used as prophylaxis. Notably, these products can be generated from either virus-naive or virus-experienced autologous or allogeneic sources, including partially matched HLA-matched third-party donors. Obstacles to effective VST treatment are donor availability and product generation time. Banking of third-party VST is an attractive way to overcome these constraints and provide products on an as-needed basis. Other developments include epitope discovery to broaden the number of viral antigens targets in a single product, the optimization of VST generation from naive donor sources, and the modification of VSTs to enhance persistence and efficacy in vivo.

Generating De Novo Antigen-specific Human T Cell Receptors by Retroviral Transduction of Centric Hemichain

T cell receptors (TCRs) are used clinically to direct the specificity of T cells to target tumors as a promising modality of immunotherapy. Therefore, cloning TCRs specific for various tumor-associated antigens has been the goal of many studies. To elicit an effective T cell response, the TCR must recognize the target antigen with optimal affinity. However, cloning such TCRs has been a challenge and many available TCRs possess sub-optimal affinity for the cognate antigen. In this protocol, we describe a method of cloning de novo high affinity antigen-specific TCRs using existing TCRs by exploiting hemichain centricity. It is known that for some TCRs, each TCRα or TCRβ hemichain do not contribute equally to antigen recognition, and the dominant hemichain is referred to as the centric hemichain. We have shown that by pairing the centric hemichain with counter-chains differing from the original counter-chain, we are able to maintain the antigen specificity, while modulating its interaction strength for the cognate antigen. Thus, the therapeutic potential of a given TCR can be improved by optimizing the pairing between the centric and counter hemichains.

Preventing stem cell transplantation-associated viral infections using T-cell therapy

Hematopoietic stem cell transplantation is the treatment of choice for many hematologic malignancies and genetic diseases. However, viral infections continue to account for substantial post-transplant morbidity and mortality. While antiviral drugs are available against some viruses, they are associated with significant side effects and are frequently ineffective. This review focuses on the immunotherapeutic strategies that have been used to prevent and treat infections over the past 20 years and outlines different refinements that have been introduced with the goal of moving this therapy beyond specialized academic centers.

Antiviral T-cell therapy

Serious viral infections are a common cause of morbidity and mortality after allogeneic stem cell transplantation. They occur in the majority of allograft recipients and are fatal in 17–20%. These severe infections may be prolonged or recurrent and add substantially to the cost, both human and financial, of the procedure. Many features of allogeneic stem cell transplantation contribute to this high rate of viral disease. The cytotoxic and immunosuppressive drugs administered pretransplant to eliminate the host hematopoietic/immune system and any associated malignancy, the delay in recapitulating immune ontogeny post‐transplant, the immunosuppressive drugs given to prevent graft versus host disease (GvHD), and the effects of GvHD itself, all serve to make stem cell transplant recipients vulnerable to disease from endogenous (latent) and exogenous (community) viruses, and to be incapable of controlling them as quickly and effectively as most normal individuals.

Virotherapy using myxoma virus prevents lethal graft-versus-host disease following xeno-transplantation with primary human hematopoietic stem cells

Graft-versus-host disease (GVHD) is a potentially lethal clinical complication arising from the transfer of alloreactive T lymphocytes into immunocompromised recipients. Despite conventional methods of T cell depletion, GVHD remains a major challenge in allogeneic hematopoietic cell transplant. Here, we demonstrate a novel method of preventing GVHD by ex vivo treatment of primary human hematopoietic cell sources with myxoma virus, a rabbit specific poxvirus currently under development for oncolytic virotherapy. This pretreatment dramatically increases post-transplant survival of immunocompromised mice injected with primary human bone marrow or peripheral blood cells and prevents the expansion of human CD3(+) lymphocytes in major recipient organs. Similar viral treatment also prevents human-human mixed alloreactive T lymphocyte reactions in vitro. Our data suggest that ex vivo virotherapy with myxoma virus can be a simple and effective method for preventing GVHD following infusion of hematopoietic products containing alloreactive T lymphocytes such as: allogeneic hematopoietic stem and progenitor cells, donor leukocyte infusions and blood transfusions.