Complex sentence: While at Harvard University, he and his colleagues made many key findings in the areas of immunoglobulin capping on B cells, host defense to Listeria monocytogenes, culminating in the discovery that MHC molecules display processed peptides to T cells.
Split into simpler sentences: While at Harvard University, he and his colleagues made important observations in the areas of immunoglobulin capping on B cells and host defenses to bacteria such as Listeria monocytogenes. That work culminated in the discovery that MHC molecules display processed peptides to T cells.