Clinical applications of mixed chimerism

Bone marrow T cells are superior to splenic T cells to induce chimeric conversion after non-myeloablative bone marrow transplantation

BACKGROUND/AIMS

The bone marrow functions not only as the primary B-lymphocyte-producing organ but also as a secondary lymphoid organ for CD4 and CD8 cell responses and a site of preferential homing and persistence for memory T cells. Bone marrow T (BM-T) cells are distinguished from peripheral blood T cells by surface phenotype, cytokine secretion profile, and immune functions. In this study, we evaluated the alloreactive potential of donor lymphocyte infusion (DLI) using BM-T cells in mixed chimerism compared to that using spleen T (SP-T) cells.

METHODS

Cells were prepared using established procedures. BM-T cells were obtained as a by-product of T-cell depletion in BM grafting and then cryopreserved for subsequent DLI. We performed DLI using BM-T cells in allogeneic mixed chimera mice on post-BMT day 21.

RESULTS

When the same dose of T cells, 5-10x10(5) (Thy1.2+), fractionated from BM and spleen were administered into mixed chimeras, the BM-T group showed complete chimeric conversion, with self-limited graft-versus-host disease (GVHD) and no pathological changes. However, the SP-T group showed persistent mixed chimerism, with pathological signs of GVHD in the liver and intestine.

CONCLUSIONS

Our results suggest that DLI using BM-T cells, even in small numbers, is more potent at inducing chimeric conversion in mixed chimerism than DLI using SP-T cells. Further study is needed to determine whether cryopreserved BM-T cells are an effective cell source for DLI to consolidate donor-dominant chimerism in clinical practice without concerns about GVHD.

Immunoregulatory effects of allogeneic mixed chimerism induced by nonmyeloablative bone marrow transplantation on chronic inflammatory arthritis and autoimmunity in interleukin-1 receptor antagonist-deficient mice

OBJECTIVE

To investigate the immunoregulatory effects of allogeneic mixed chimerism induced by T cell-depleted, nonmyeloablative bone marrow transplantation (BMT) on chronic inflammatory arthritis and autoimmunity in mice deficient in interleukin-1 receptor antagonist (IL-1Ra).

METHODS

IL-1Ra(-/-) mice (H-2K(d)) were treated with antibody to asialoganglioside G(M1) (anti-natural killer cell), total body irradiation (500 cGy), and T cell-depleted, nonmyeloablative BMT derived from C57BL/6 mice (H-2K(b)). Engraftment and chimerism were evaluated in peripheral blood, lymph nodes, and spleen by multicolor flow cytometry. The severity of arthritis was evaluated by clinical scoring and histopathologic assessment. Levels of IgG1 and IgG2a subtypes of anti-type II collagen (anti-CII) antibodies were measured in serum samples. After T cells were stimulated with CII, ovalbumin, and phytohemagglutinin, T cell proliferative responses and levels of cytokine production (interferon-gamma [IFNgamma], tumor necrosis factor alpha [TNFalpha], interleukin-10 [IL-10], and IL-17) were assayed in culture supernatants.

RESULTS

All IL-1Ra(-/-) mice receiving BMT showed marked improvement in arthritis within 3 weeks, as well as successful induction of mixed chimerism. These mice showed higher levels of IgG1, and lower levels of IgG2a anti-CII antibodies and weaker T cell proliferative responses than did mice in the control groups (either no treatment or conditioning alone without bone marrow rescue). In mixed chimeras, the levels of IFNgamma, TNFalpha, and IL-17 produced from CII-stimulated T cells were significantly suppressed and IL-10 production was significantly higher as compared with controls.

CONCLUSION

The introduction of allogeneic mixed chimerism showed a strong immunoregulatory potential to correct established chronic inflammatory arthritis and autoimmunity originating from a dysregulated proinflammatory cytokine network.

Split chimerism after allogeneic bone marrow transplantation in Chediak-Higashi syndrome

Chediak-Higashi Syndrome (CHS) is a hereditary multiorgan disease associated with a lymphoproliferative disorder termed 'accelerated phase' (AP). As AP is often life-threatening, hematopoietic stem cell transplantation has been proposed as the only curative treatment for CHS. Here, we report a 1-year-old Japanese boy with CHS who received an HLA-matched unrelated BMT at the AP stage, which resulted in split chimerism. We evaluated the chimerism status of isolated leukocytes and found that only a limited population of T and NK cells was of donor origin and the majority of these and other hematopoietic cells was of host origin. Clinical outcome was successful, and the patient is currently alive and well, free of AP and serious infections more than 18 months after BMT.

Myeloablation enhances engraftment of transduced murine hematopoietic cells, but does not influence long-term expression of the transgene

To investigate to what extent myeloablation, graft size, and ex vivo manipulation influence the engraftment and long-term survival of transduced murine hematopoietic cells, groups of C57BL/6J (CD45.2) mice receiving total body irradiation (TBI) (1-9 Gy) or no irradiation were transplanted with either transduced bone marrow (BM) cells, at two cell doses, or with fresh BM cells from B6/SJL (CD45.1) congenic mice. Short (40 days) and long-term (5 months) engraftment and transgene expression were measured by FACS analysis. No donor cells were detected in the hematopoietic tissues of non-myeloablated mice, whereas in the irradiated animals, levels of engraftment correlated well with the dose of TBI administered. Similar percentages of transgene-expressing cells were found in the grafted hematopoietic cells of all groups of mice, regardless of the dose of TBI administered or the level of engraftment achieved. This suggests that the engrafted animals could become tolerant to the transgene product (enhanced green fluorescent protein, EGFP). Our results indicate that TBI facilitates the engraftment of manipulated hematopoietic cells in a dose-dependent manner, that mice engrafted with EGFP(+) hematopoietic cells probably acquire tolerance to EGFP, and that increasing the graft size and reducing the ex vivo manipulation required for retroviral gene transfer of hematopoietic cells also enhances their engrafting potential.

Critical review on non-myeloablative stem cell transplantation (NST)

Allogeneic stem cell transplantation is an established treatment modality for a variety of hematologic malignancies. Unfortunately, it carries a high risk of complications and toxicities related to the intensive preparative regimen which is traditionally used for pre-transplant myeloablation and the graft versus host disease, which may be life threatening. Thus allogeneic stem cell transplantation has been used only for younger patients with a good performance status, excluding many other potential candidates due to advanced age or comorbid conditions. Using reduced intensity preparative regimens for allogeneic stem cell transplantation (non-myeloablative stem cell transplantation (NST)) researchers attempted to overcome these barriers in patients' selection and tried to make hematopoietic stem cell (HSC) transplantation a safer procedure. The well-described graft versus malignancy effect would be the most curative element in this treatment. After more than 5 years of cumulative clinical experience, we know that NST is a feasible treatment option for patients with suboptimal performance status and is mostly effective in slow proliferating malignancies, which gives time for a graft versus malignancy effect to take place. Additionally achievement of stable donor cell engraftment with NSTs provides a platform for adoptive immune cell treatments and is promising for extended indications of stem cell transplantation in the future.

Update on non-myeloablative stem cell transplantation for hematologic malignancies

Allogeneic stem cell transplantation is an established treatment modality for a variety of hematologic malignancies. Unfortunately it carries a high risk of complications and toxicities related to the intensive preparative regimen which is traditionally used for pre-transplant myeloablation and the graft versus host disease, which may be life threatening. Thus allogeneic stem cell transplantation has been used only for younger patients with a good performance status, excluding many other potential candidates due to advanced age or comorbid conditions. Non ablative or reduced intensity preparative regimens for allogeneic stem cell transplantation (NST) have been proposed as a strategy that would allow exploiting the graft versus tumor effect of allogeneic transplantation without the toxicity of myeloablative therapy. After more than five years of cumulative clinical experience, it is now well established that NST is a feasible treatment option for patients with suboptimal performance status and is mostly effective in slow proliferating malignancies, which gives time for a graft versus malignancy effect to take place. Additionally achievement of stable donor cell engraftment with NSTs provides a platform for adoptive immune cell treatments and may allow to extend indications of stem cell transplantation in the future.

Bone marrow cell graft engineering: from bench to bedside

Bone marrow transplantation (BMT) has the potential to treat hemoglobinopathies (sickle cell and thalassemia) autoimmunity (diabetes, lupus, multiple sclerosis, rheumatoid arthritis, Crohn's colitis) and enzyme deficiency states. Graft versus host disease (GVHD) is a major complication and limitation to the therapeutic application of BMT. There have been many clinical trials and experimental animal models that have attempted to control GVHD through the engineering of the donor bone marrow cells (BMC). Historically, several methods have demonstrated effectiveness in controlling GVHD; however they were also associated with a marked increase in the rate of graft failure. Highly purified hematopoietic stem cells (HSC) engraft quite readily in genetically-matched recipients while they do not engraft as easily in MHC-disparate recipients. The numbers of HSC must be increased 100-200 fold in order to overcome the allogeneic barrier. We were the first to phenotypically and to functionally characterize a novel cell in the bone marrow that enables engraftment of highly purified HSC in allogeneic recipients. The discovery of graft facilitating cell populations has resulted in the restoration of the engraftment-potential of purified HSC between genetically-disparate individuals. The addition of facilitating cells (FC) to T cell-depleted BMC grafts results in allogeneic engraftment without GVHD or graft failure. New strategies of BMC engineering that retain FC and HSC but avoid GVHD have allowed successful engraftment in mismatched and older recipients. These techniques have expanded the therapeutic potential of BMT to virtually every candidate as well as to non-malignant diseases in which the morbidity associated with conventional BMT could not be accepted. This article reviews the transition of the FC technology from bench to bedside and discuss the potentially broad-reaching applications of BMT and mixed chimerism.