Mocravimod, a Selective Sphingosine-1-Phosphate Receptor Modulator, in Allogeneic Hematopoietic Stem Cell Transplantation for Malignancy.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the sole curative option for patients with acute myelogenous leukemia. Outcomes are limited by leukemia relapse, graft-versus-host disease (GVHD), and abnormal immune reconstitution. Mocravimod (KRP203) is an oral sphingosine-1-phosphate receptor (S1PR) modulator that blocks the signal required by T cells to egress from lymph nodes and other lymphoid organs. Mocravimod retains T cell effector function, a main differentiator to immunosuppressants. In preclinical models, mocravimod improves survival by maintaining graft-versus-leukemia (GVL) activity while reducing GVHD. In patients undergoing allo-HSCT for hematological malignancies, mocravimod is postulated to prevent GVHD by redistributing allogeneic donor T cells to lymphoid tissues while allowing a sufficient GVL effect in the lymphoid, where malignant cells usually reside. The primary objective of this study was to assess the safety and tolerability of mocravimod in patients undergoing allo-HSCT for hematologic malignancies. Secondary objectives were to determine the pharmacokinetic profiles of mocravimod and its active metabolite mocravimod-phosphate in this patient group, as well as to assess GVHD-free, relapse free survival at 6 months after the last treatment. In this 2-part, single- and 2-arm randomized, open-label trial, we evaluated the safety, tolerability, and pharmacokinetics of mocravimod in allo-HSCT recipients (ClinicalTrials.gov identifier NCT01830010). Patients received either 1 mg or 3 mg mocravimod per day on top of standard of care GVHD prophylaxis with either cyclosporine A/methotrexate or tacrolimus/methotrexate. We found that mocravimod can be safely added to standard treatment regimens in patients with hematologic malignancies requiring allo-HSCT. Mocravimod resulted in a significant reduction of circulating lymphocyte numbers and had no negative impact on engraftment and transplantation outcomes. Our results indicate that mocravimod is safe and support a larger study to investigate its efficacy in a homogeneous acute myelogenous leukemia patient population undergoing allo-HSCT.

Marginal zone macrophages and immune responses against viruses.

The effective establishment of antiviral protection requires a coordinated interplay between the innate and adaptive immune system. Using osteopetrotic (op(-/-)) mice, this study investigated the influence of marginal zone macrophages in controlling and initiating a protective immune response against a cytopathic vs a non- or low-cytopathic virus. Despite the generation of potent adaptive immune responses, antiviral protection against cytopathic vesicular stomatitis virus critically depended on the presence of marginal zone macrophages. Infection with low doses (100 PFU) of non- or low-cytopathic lymphocytic choriomeningitis virus was rarely cleared and usually resulted in a carrier state in the majority of mice. This shows that the early innate immune system provides an important preparatory phase to the adaptive immune system and is particularly important for antiviral protection.