RAD51AP1 Loss Attenuates Colorectal Cancer Stem Cell Renewal and Sensitizes to Chemotherapy.

DNA damage, induced by either chemical carcinogens or environmental pollutants, plays an important role in the initiation of colorectal cancer. DNA repair processes, however, are involved in both protecting against cancer formation, and also contributing to cancer development, by ensuring genomic integrity and promoting the efficient DNA repair in tumor cells, respectively. Although DNA repair pathways have been well exploited in the treatment of breast and ovarian cancers, the role of DNA repair processes and their therapeutic efficacy in colorectal cancer is yet to be appreciably explored. To understand the role of DNA repair, especially homologous recombination (HR), in chemical carcinogen-induced colorectal cancer growth, we unraveled the role of RAD51AP1 (RAD51-associated protein 1), a protein involved in HR, in genotoxic carcinogen (azoxymethane, AOM)-induced colorectal cancer. Although AOM treatment alone significantly increased RAD51AP1 expression, the combination of AOM and dextran sulfate sodium (DSS) treatment dramatically increased by several folds. RAD51AP1 expression is found in mouse colonic crypt and proliferating cells. RAD51AP1 expression is significantly increased in majority of human colorectal cancer tissues, including BRAF/KRAS mutant colorectal cancer, and associated with reduced treatment response and poor prognosis. Rad51ap1-deficient mice were protected against AOM/DSS-induced colorectal cancer. These observations were recapitulated in a genetically engineered mouse model of colorectal cancer (ApcMin /+ ). Furthermore, chemotherapy-resistant colorectal cancer is associated with increased RAD51AP1 expression. This phenomenon is associated with reduced cell proliferation and colorectal cancer stem cell (CRCSC) self-renewal. Overall, our studies provide evidence that RAD51AP1 could be a novel diagnostic marker for colorectal cancer and a potential therapeutic target for colorectal cancer prevention and treatment. IMPLICATIONS: This study provides first in vivo evidence that RAD51AP1 plays a critical role in colorectal cancer growth and drug resistance by regulating CRCSC self-renewal.

Revisiting Role of Vaccinations in Donors, Transplant Recipients, Immunocompromised Hosts, Travelers, and Household Contacts of Stem Cell Transplant Recipients.

Vaccination is an effective strategy to prevent infections in immunocompromised hematopoietic stem cell transplant recipients. Pretransplant vaccination of influenza, pneumococcus, Haemophilus influenza type b, diphtheria, tetanus, and hepatitis B, both in donors and transplant recipients, produces high antibody titers in patients compared with recipient vaccination only. Because transplant recipients are immunocompromised, live vaccines should be avoided with few exceptions. Transplant recipients should get inactive vaccinations when possible to prevent infection. This includes vaccination against influenza, pneumococcus, H. influenza type b, diphtheria, tetanus, pertussis, meningococcus, measles, mumps, rubella, polio, hepatitis A, human papillomavirus, and hepatitis B. Close contacts of transplant recipients can safely get vaccinations (inactive and few live vaccines) as per their need and schedule. Transplant recipients who wish to travel may need to get vaccinated against endemic diseases that are prevalent in such areas. There is paucity of data on the role of vaccinations for patients receiving novel immunotherapy such as bispecific antibodies and chimeric antigen receptor T cells despite data on prolonged B cell depletion and higher risk of opportunistic infections.