Autologous apoptotic cells preceding transplantation enhance survival in lethal murine graft-versus-host models.

Acute graft-versus-host disease (GVHD) is induced by alloreactivity of donor T cells toward host antigens presented on antigen-presenting cells (APCs). Apoptotic cells are capable of inducing tolerance by altering APC maturation. Apoptosis can be induced by extracorporeal photopheresis (ECP). We demonstrate that the use of ECP as a prophylaxis prior to conditioning significantly improves survival (P < .0001) after bone marrow transplantation (BMT) by inhibiting the initiation phase of acute GVHD in a murine BMT model. ECP-treated autologous splenocytes resulted in immune tolerance in the host, including reduced dendritic cell activation with decreased nuclear factor-κB engagement, increased regulatory T-cell (Treg) numbers with enhanced expression of cytolytic T lymphocyte-associated antigen 4, potentiating their suppressive function. The protective effect required host production of interleukin-10 and host Tregs. Conventional T cells that entered this tolerant environment experienced reduced proliferation, as well as a reduction of tissue homing and expression of activation markers. The induction of this tolerant state by ECP was obviated by cotreatment with lipopolysaccharide, suggesting that the inflammatory state of the recipient prior to treatment would play a role in potential clinical translation. The use of prophylactic ECP may provide an alternative and safe method for immunosuppression in the bone marrow transplant setting.

Role of lymphocyte activation gene-3 (Lag-3) in conventional and regulatory T cell function in allogeneic transplantation.

Lag-3 has emerged as an important molecule in T cell biology. We investigated the role of Lag-3 in conventional T cell (Tcon) and regulatory T cell (Treg) function in murine GVHD with the hypothesis that Lag-3 engagement diminishes alloreactive T cell responses after bone marrow transplantation. We demonstrate that Lag-3 deficient Tcon (Lag-3(-/-) Tcon) induce significantly more severe GVHD than wild type (WT) Tcon and that the absence of Lag-3 on CD4 but not CD8 T cells is responsible for exacerbating GVHD. Lag-3(-/-) Tcon exhibited increased activation and proliferation as indicated by CFSE and bioluminescence imaging analyses and higher levels of activation markers such as CD69, CD107a, granzyme B, and Ki-67 as well as production of IL-10 and IFN-g early after transplantation. Lag-3(-/-) Tcon were less responsive to suppression by WT Treg as compared to WT Tcon. The absence of Lag-3, however, did not impair Treg function as both Lag-3(-/-) and WT Treg equally suppress the proliferation of Tcon in vitro and in vivo and protect against GVHD. Further, we demonstrate that allogeneic Treg acquire recipient MHC class II molecules through a process termed trogocytosis. As MHC class II is a ligand for Lag-3, we propose a novel suppression mechanism employed by Treg involving the acquisition of host MHC-II followed by the engagement of Lag-3 on T cells. These studies demonstrate for the first time the biologic function of Lag-3 expression on conventional and regulatory T cells in GVHD and identify Lag-3 as an important regulatory molecule involved in alloreactive T cell proliferation and activation after bone marrow transplantation.

Mast cells suppress murine GVHD in a mechanism independent of CD4+CD25+ regulatory T cells.

To investigate the role of mast cells in hematopoietic cell transplantation, we assessed graft-versus-host disease (GVHD) in C57BL/6-Kit(W-sh/W-sh) recipients, which virtually lack mast cells, compared with C57BL/6 WT recipients. GVHD was severely exacerbated in C57BL/6-Kit(W-sh/W-sh) mice (median survival time = 13 vs 60 days in wild-type [WT] mice; P < .0001). The increased mortality risk in C57BL/6-Kit(W-sh/W-sh) hosts correlated with increased T-cell numbers in lymph nodes, liver, and gastrointestinal tract sites, as indicated by bioluminescence imaging (P < .001). We did not detect any deficit in the number or function of CD4(+)CD25(+) regulatory T cells (Tregs) in C57BL/6-Kit(W-sh/W-sh) mice. Furthermore, Tregs were equally effective at reducing GVHD in C57BL/6-Kit(W-sh/W-sh) recipients compared with WT recipients containing mast cells. Furthermore, we found that survival of C57BL/6-Kit(W-sh/W-sh) mice during GVHD was significantly improved if the mice were engrafted with bone marrow-derived cultured mast cells from WT C57BL/6 mice but not from interleukin (IL)-10-deficient C57BL/6 mice. These data indicate that the presence of mast cells can significantly reduce GVHD independently of Tregs, by decreasing conventional T-cell proliferation in a mechanism involving IL-10. These experiments support the conclusion that mast cells can mediate a novel immunoregulatory role during hematopoietic cell transplantation.

IL-17 gene ablation does not impact Treg-mediated suppression of graft-versus-host disease after bone marrow transplantation.

Regulatory T cell (Treg) immunotherapy is a promising strategy for the treatment of graft rejection responses and autoimmune disorders. Our and other laboratories have shown that the transfer of highly purified CD4(+)CD25(+)Foxp3(+) natural Treg can prevent lethal graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation across both major and minor histocompatibility barriers. However, recent evidence suggests that the Treg suppressive phenotype can become unstable, a phenomenon that can culminate in Treg conversion into IL-17-producing cells. We hypothesized that the intense proinflammatory signals released during an ongoing alloreaction might redirect a fraction of the transferred Treg to the Th17 cell fate, thereby losing immunosuppressive potential. We therefore sought to evaluate the impact of Il17 gene ablation on Treg stability and immunosuppressive capacity in a major MHC mismatch model. We show that although Il17 gene ablation results in a mildly enhanced Treg immunosuppressive ability in vitro, such improvement is not observed when IL-17-deficient Treg are used for GVHD suppression in vivo. Similarly, when we selectively blocked IL-1 signaling in Treg, that was shown to be necessary for Th17 conversion, we did not detect any improvement on Treg-mediated GVHD suppressive ability in vivo. Furthermore, upon ex vivo reisolation of transferred wild-type Treg, we detected little or no Treg-mediated IL-17 production upon GVHD induction. Our results indicate that blocking Th17 conversion does not affect the GVHD suppressive ability of highly purified natural Treg in vivo, suggesting that IL-17 targeting is not a valuable strategy to improve Treg immunotherapy after hematopoietic cell transplantation.

Rapamycin and IL-2 reduce lethal acute graft-versus-host disease associated with increased expansion of donor type CD4+CD25+Foxp3+ regulatory T cells.

Previous work has demonstrated that both rapamycin (RAPA) and IL-2 enhance CD4⁺CD25⁺Foxp3⁺ regulatory T-cell (Treg) proliferation and function in vitro. We investigated whether the combination of RAPA plus IL-2 could impact acute GVHD induction after bone marrow transplantation (BMT). RAPA plus IL-2 resulted in improved survival and a reduction in acute GVHD lethality associated with an increased expansion of donor type CD4⁺Foxp3⁺ Tregs and reduced CD4⁺CD25⁻ conventional T cells (Tcons). RAPA plus IL-2, but not either drug alone, increased both expansion of donor natural Tregs and conversion of induced Tregs from donor CD25⁻ Tcons while IL-2 alone increased conversion of Tregs from CD25⁻ Tcon. RAPA plus IL-2 treatment resulted in less production of IFN-γ and TNF, cytokines known to be important in the initiation of acute GVHD. These studies indicate that the pharmacologic stimulation of T cells with IL-2 and the suppression of Tcon proliferation with RAPA result in a selective expansion of functional Tregs and suppression of acute GVHD.

Low doses of natural killer T cells provide protection from acute graft-versus-host disease via an IL-4-dependent mechanism.

CD4(+) natural killer T (NKT) cells, along with CD4(+)CD25(+) regulatory T cells (Tregs), are capable of controlling aberrant immune reactions. We explored the adoptive transfer of highly purified (> 95%) CD4(+)NKT cells in a murine model of allogeneic hematopoietic cell transplantation (HCT). NKT cells follow a migration and proliferation pattern similar to that of conventional T cells (Tcons), migrating initially to secondary lymphoid organs followed by infiltration of graft-versus-host disease (GVHD) target tissues. NKT cells persist for more than 100 days and do not cause significant morbidity or mortality. Doses of NKT cells as low as 1.0 × 10(4) cells suppress GVHD caused by 5.0 × 10(5) Tcons in an interleukin-4 (IL-4)-dependent mechanism. Protective doses of NKT cells minimally affect Tcon proliferation, but cause significant reductions in interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) production by donor Tcons and in skin, spleen, and gastrointestinal pathology. In addition, NKT cells do not impact the graft-versus-tumor (GVT) effect of Tcons against B-cell lymphoma-1 (BCL-1) tumors. These studies elucidate the biologic function of donor-type CD4(+)NKT cells in suppressing GVHD in an allogeneic transplantation setting, demonstrating clinical potential in reducing GVHD in HCT.

Tumor detection using folate receptor-targeted imaging agents.

Folate receptors are up-regulated on a variety of human cancers, including cancers of the breast, ovaries, endometrium, lungs, kidneys, colon, brain, and myeloid cells of hematopoietic origin. This over-expression of folate receptors (FR) on cancer tissues can be exploited to target folate-linked imaging and therapeutic agents specifically to FR-expressing tumors, thereby avoiding uptake by most healthy tissues that express few if any FR. Four folate-targeted therapeutic drugs are currently undergoing clinical trials, and several folate-linked chemotherapeutic agents are in late stage preclinical development. However, because not all cancers express FR, and because only FR-expressing cancers respond to FR-targeted therapies, FR-targeted imaging agents have been required to select patients with FR-expressing tumors likely to respond to folate-targeted therapies. This review focuses on recent advances in the use of the vitamin folic acid to target PET agents, gamma-emitters, MRI contrast agents and fluorescent dyes to FR(+) cancers for the purpose of diagnosing and imaging malignant masses with improved specificity and sensitivity.

In vivo trafficking and survival of cytokine-induced killer cells resulting in minimal GVHD with retention of antitumor activity.

Cytokine-induced killer (CIK) cells are ex vivo-expanded T lymphocytes expressing both natural killer (NK)- and T-cell markers. CIK cells are cytotoxic against autologous and allogeneic tumors. We previously showed that adoptive transfer of allogeneic CIK cells in a murine model caused minimal graft-versus-host disease (GVHD). However, the precise mechanism of reduced GVHD is not fully understood. Therefore, we evaluated the trafficking and survival of luciferase-expressing CIK cells in an allogeneic bone marrow transplant model. The initial trafficking patterns of CIK cells were similar to conventional T cells that induced GVHD; however, CIK cells infiltrated GVHD target tissues much less and transiently. CIK cells accumulated and persisted in tumor sites, resulting in tumor eradication. We evaluated different properties of CIK cells compared with conventional T cells, demonstrating a slower division rate of CIK cells, higher susceptibility to apoptosis, persistent increased expression of interferon gamma (IFN-gamma), and reduced acquisition of homing molecules required for entry of cells into inflamed GVHD target organs that lack expression of NKG2D ligands recognized by CIK cells. Due to these properties, allogeneic CIK cells had reduced expansion and caused less tissue damage. We conclude that CIK cells have the potential to separate graft-versus-tumor effects from GVHD.

Low-dose radiation potentiates the therapeutic efficacy of folate receptor-targeted hapten therapy.

PURPOSE: Human cancers frequently overexpress a high-affinity cell-surface receptor for the vitamin folic acid. Highly immunogenic haptens can be targeted to folate receptor-expressing cell surfaces by administration of folate-hapten conjugates, rendering the decorated tumor cell surfaces more recognizable by the immune system. Treatment of antihapten-immunized mice with folate-hapten constructs results in elimination of moderately sized tumors by the immune system. However, when subcutaneous tumors exceed 300 mm(3) before initiation of therapy, antitumor activity is significantly decreased. In an effort to enhance the efficacy of folate-targeted hapten immunotherapy (FTHI) against large tumors, we explored the combination of targeted hapten immunotherapy with low-dose radiotherapy. METHODS AND MATERIALS: Mice bearing 300-mm(3) subcutaneous tumors were treated concurrently with FTHI (500 nmol/kg of folate conjugated to fluorescein isothiocyanate, 20,000 U/dose of interleukin 2, and 25,000 U/dose of interferon alpha) and low-dose radiotherapy (3 Gy/dose focused directly on the desired tumor mass). The efficacy of therapy was evaluated by measuring tumor volume. RESULTS: Tumor growth analyses show that radiotherapy synergizes with FTHI in antihapten-immunized mice, thereby allowing for cures of animals bearing tumors greater than 300 mm(3). More importantly, nonirradiated distal tumor masses in animals containing locally irradiated tumors also showed improved response to hapten immunotherapy, suggesting that not all tumor lesions must be identified and irradiated to benefit from the combination therapy. CONCLUSIONS: These results suggest that simultaneous treatment with FTHI and radiation therapy can enhance systemic antitumor activity in tumor-bearing mice.