Adoptive precursor cell therapy to enhance immune reconstitution after hematopoietic stem cell transplantation

An ISCT Stem Cell Engineering Committee Position Statement on Immune Reconstitution: the importance of predictable and modifiable milestones of immune reconstitution to transplant outcomes

Allogeneic stem cell transplantation is a potentially curative therapy for some malignant and non-malignant disease. There have been substantial advances since the approaches first introduced in the 1970s, and the development of approaches to transplant with HLA incompatible or alternative donors has improved access to transplant for those without a fully matched donor. However, success is still limited by morbidity and mortality from toxicity and imperfect disease control. Here we review our emerging understanding of how reconstitution of effective immunity after allogeneic transplant can protect from these events and improve outcomes. We provide perspective on milestones of immune reconstitution that are easily measured and modifiable.

Greater than the sum of their parts: combination strategies for immune regeneration following allogeneic hematopoietic stem cell transplantation

Cytoreductive conditioning regimes designed to allow for successful allogeneic hematopoietic stem cell transplantation (allo-HSCT) paradoxically are also detrimental to recovery of the immune system in general but lymphopoiesis in particular. Post-transplant immune depletion is particularly striking within the T cell compartment which is exquisitely sensitive to negative regulation, evidenced by the profound decline in thymic function with age. As a consequence, regeneration of the immune system remains a significant unmet clinical need. Over the past decade studies have revealed several promising therapeutic strategies to address ineffective lymphopoiesis and post-transplant immune deficiency. These include the use of cytokines such as IL-7, IL-12 and IL-15; growth factors and hormones like keratinocyte growth factor (KGF), insulin-like growth factor (IGF)-1 and growth hormone (GH); adoptive transfer of ex vivo-generated precursor T cells (pre-T) and sex steroid ablation (SSA). Moreover, recently several novel approaches have been proposed to generate whole thymii ex vivo using stem cell technologies and bioscaffolds. Increasingly, however, when transferred to the clinic, these strategies alone are not sufficient to restore thymopoiesis in all patients leading to the potential of combination strategies as a way to reign in non-responders. Synergistic enhancement in combination may be due to differential targets may therefore be effective in improving clinical outcomes in the transplant settings as well as in other lymphopenic states induced by high dose chemotherapy/radiation therapy or HIV, and may also be useful in improving responses to vaccination and augmenting anti-tumor immunotherapy.

Immune reconstitution after allogeneic transplantation and expanding options for immunomodulation: an update

Allogeneic hematopoietic stem cell transplantation (HSCT) has advanced to a common procedure for treating also older patients with malignancies and immunodeficiency disorders by redirecting the immune system. Unfortunately, cure is often hampered by relapse of the underlying disease, graft-versus-host disease, or severe opportunistic infections, which account for the majority of deaths after HSCT. Enhancing immune reconstitution is therefore an area of intensive research. An increasing variety of approaches has been explored preclinically and clinically: the application of cytokines, keratinocyte growth factor, growth hormone, cytotoxic lymphocytes, and mesenchymal stem cells or the blockade of sex hormones. New developments of allogeneic HSCT, for example, umbilical cord blood or haploidentical graft preparations leading to prolonged immunodeficiency, have further increased the need to improve immune reconstitution. Although a slow T-cell reconstitution is regarded as primarily responsible for deleterious infections with viruses and fungi, graft-versus-host disease, and relapse, the importance of innate immune cells for disease and infection control is currently being reevaluated. The groundwork has been prepared for the creation of individualized therapy partially based on genetic features of the underlying disease. We provide an update on selected issues of development in this fast evolving field; however, we do not claim completeness.

Enhancing T cell reconstitution after hematopoietic stem cell transplantation: a brief update of the latest trends

Hematopoietic stem cell transplantation (HSCT) is associated with a period of immune incompetence that particularly affects the T cell lineage. Strategies to enhance T cell reconstitution could significantly improve the survival of HSCT recipients by decreasing the incidence of fatal infectious complications and by enhancing graft-versus-tumor activity. In recent years, a variety of promising strategies have been established in preclinical models to improve T cell recovery in particular after allogeneic T cell-depleted HSCT, without aggravating graft-versus-host disease while preserving or even improving graft-versus-tumor activity. These therapies include treatment with keratinocyte growth factor (KGF), growth hormone (GH), LHRH agonists, interleukin 7 (IL-7) and interleukin 15 (IL-15). Thanks to the establishment of Notch-based culture systems, adoptive cellular therapies with T lineage-committed precursor cells have become feasible, since early T cell progenitors can now easily be generated in vitro in large quantities and have been proven to be very effective in enhancing T cell reconstitution and anti-tumor activity after allogeneic T cell-depleted HSCT. The translation of most of these strategies into clinical trials is likely and in some cases Phase I/II studies are already underway.