Pretransplant treatment of donors with immunomodulators to control graft-versus-host disease (GVHD) in transplant recipients

Antigen-Specific Priming is Dispensable in Depletion of Apoptosis-Sensitive T Cells for GvHD Prophylaxis

Prophylactic approaches to graft versus host disease (GvHD) have employed both phenotypic reduction of T cells and selective elimination of host-primed donor T cells in vitro and in vivo. An additional approach to GvHD prophylaxis by functional depletion of apoptosis-sensitive donor T cells without host-specific sensitization ex vivo showed remarkable reduction in GHD incidence and severity. We address the role and significance of antigen-specific sensitization of donor T cells and discuss the mechanisms of functional T cell purging by apoptosis for GvHD prevention. Host-specific sensitization is dispensable because migration is antigen-independent and donor T cell sensitization is mediated by multiple and redundant mechanisms of presentation of major and minor histocompatibility complex and tissue antigens by donor and host antigen-presenting cells. Our data suggest that potential murine and human GvH effectors reside within subsets of preactivated T cells susceptible to negative regulation by apoptosis prior to encounter of and sensitization to specific antigens.

A safety study of a B-class CpG ODN in Sprague-Dawley rats

Oligodeoxynucleotides containing CpG motifs (CpG ODNs) are potent immune activators and are being tested as anti-tumor, antimicrobial agents and as adjuvants in vaccines. Little has been reported, however, about the systematic and comprehensive safety evaluation on repeated CpG ODN administration. To investigate the safety profile of a newly developed CpG ODN, CpG 684, we conducted a 28-day repeated dose toxicity study in rats, at dose levels of 5, 20 and 150 µg CpG 684 per rat. No abnormalities in clinical observations, growth, urinalysis and bone marrow cell counts were found in CpG 684 treated rats. CpG 684 was proved biologically active, capable of up-regulating the expressions of CD40 and CD86 molecules. The monocyte numbers were increased at the dose levels of 20 and 150 µg per rat. The spleen weights were increased in female rats at the dose level of 150 µg per rat. Microscopically, 5, 20 and 150 µg per rat CpG 684 caused local inflammatory cell infiltration and hyperplasia of fibrous tissue at injection sites; the treatment of 5 and 150 µg per rat CpG 684 induced enhanced inflammatory reaction in inguinal lymphoid tissue, and the dose of 150 µg per rat induced cell hyperplasia in white pulp of spleen and white pulp expansion. CpG 684 at 150 µg per rat led to decreases in peripheral lymphocyte, serum globulin, glucose, alkaline phosphatase and K+ levels in female rats, and induced the decrease in serum albumin and total protein in rats of both sexes. The data from this study will provide an important reference for developing CpG 684 as an adjuvant for vaccines of human use.

Immunoregulation of GVHD by triggering the innate immune system with CpG

Stimulation of Toll-like receptors by oligodeoxynucleotide sequences containing a CpG motif provides signals capable of triggering the innate and adaptive immune systems, thereby leading either to stimulation or suppression of immunoreactivities. Similar immunoregulatory capabilities are necessary for achieving the fine balance between engraftment and graft-versus-host disease required in the setup of allogeneic cell therapy. Ligation of CpG to its Toll-like receptors can be accomplished by treatment of the host or pretransplant treatment of the donor in vivo. These different strategies are presented in this review, which summarizes the attempts to maximize beneficial alloreactivity against malignant or other undesirable host cells, while controlling graft-versus-host disease.

Induction of graft-versus-leukemia (GVL) effect without graft-versus-host disease (GVHD) by pretransplant donor treatment with immunomodulators

Pretransplant donor treatment with immunomodulators such as complete Freund's adjuvant (CFA) or oligodeoxynucleotide sequences expressing CpG motifs (CpG), was applied in sublethally irradiated host mice inoculated with murine models of mammary carcinoma (4T1) or B cell leukemia (BCL1). Spleen cells or IL-2 activated splenocytes (lymphokine activated killer [LAK]) derived from donor mice treated with CpG emulsified in incomplete Freund's adjuvant (IFA), (CpG + IFA) did not cause graft-versus-host disease (GVHD), but were not efficient enough to induce a significant graft-versus-tumor (GVT) response against 4T1 cells. In contrast, an efficient graft-versus-leukemia (GVL) effect was evident in BCL1-bearing mice inoculated with spleen cells from donors pretreated with CFA or CpG + IFA. Pretransplant donor treatment with CFA prolonged survival to a median of 62 days with 3 of 27 mice remaining GVHD- and leukemia-free for >200 days, compared to GVHD-related death of all mice inoculated with naïve cells (median 17 days), or leukemia-related death of all mice inoculated with leukemia cells (median of 27 days). Pretransplant donor treatment with CpG + IFA exerted a more efficient GVL effect with reduced GVHD resulting in 12 of 26 GVHD- and leukemia-free survivors for >200 days. Our results suggest that it may be possible to prevent GVHD while sparing an efficient GVL effect by using pretransplant donor treatment with immunomodulators prior to allogeneic stem cell transplantation and/or donor lymphocyte infusions in hematologic malignancies.

CpG-induced myeloid CD11b+Gr-1+ cells efficiently suppress T cell-mediated immunoreactivity and graft-versus-host disease in a murine model of allogeneic cell therapy

Transplantation of mismatched allografts in irradiated recipients results in lethal graft- versus-host disease (GVHD). In our study, pretransplantation donor treatment with CpG, administered either alone or emulsified in incomplete Freund's adjuvant, efficiently prevented GVHD in sublethally irradiated recipients of haploidentical (H-2(b) into H-2(b/d)) and fully mismatched (H-2(b) into H-2(d)) allografts. CpG treatment of donor mice caused an accumulation of double-positive CD11bGr-1 cells in their blood and spleens, whereas treatment with CpG+IFA resulted in an even greater accumulation of these cells. Isolated CD11b(+) cells from the spleens of CpG+IFA-treated mice efficiently suppressed alloreactivity in vitro (> 92%), as determined by co-culturing these cells in mixed lymphocyte reactions. After CpG+IFA treatment, a T cell-depleted fraction enriched with CD11b(+)Gr-1(+) cells, acting as myeloid suppressor cells, was able to efficiently prevent GVHD induced by naïve T cells in the sublethally irradiated recipients: 20/21 mice remained GVHD-free survivors for more than 200 days. Splenocytes from CpG+IFA-treated mice displayed enhanced interleukin (IL)-6, IL-10, and interferon-gamma production, reduced T cell allogeneic and mitogenic responses, as well as failure of T cells to induce GVHD. In summary, CpG treatment led to impaired T cell function, enriched myeloid suppressor cells and regulatory cytokine production, which together appear to suppress alloreactivity and protect against the development of GVHD. We hypothesize that similar immunoregulatory effects could be applied experimentally in a clinical setting when inhibition of alloreactivity is required in recipients of stem cell allografts.