Influenza virus is an important cause of morbidity in the transplant population and can lead to viral and bacterial pneumonia. Although the annual influenza vaccine is recommended for organ transplant patients, studies have shown that the standard inactivated influenza vaccine has poor immunogenicity in this population. One major hurdle in the evaluation of the response of influenza vaccine in immunocompromised patients is the lack of correlation between humoral response and efficacy of the vaccine. In patients with poor immune responses, cellular immunity may have a better correlation than humoral immunity with vaccine protection. We plan to assess the utility of 3 assays that evaluate the cell-mediated immune response (granzyme B, interleukin-10 (IL-10), and interferon-gamma (IFN-)) after influenza vaccine in kidney transplant recipients. Results from this study have the potential to directly improve patient care. The new monitoring assays may more accurately determine the risk for development of influenza infection, and therefore allowing a better prevention strategy.