 Jegasothy helped develop an improved treatment for a rare kind of cancer known as cutaneous T-cell lymphoma.Jegasothy and his colleagues at Yale University established the standard photopheresis technique used to treat serious cases of cutaneous T-cell lymphoma
He also aided in the study of immunobullous diseases, which is when the immune system attacks the skin and causes it to blister and fall off.He helped in the development of a topical form of FK506, which is an anti-rejection drug invented by organ transplant researchers at Pittsburgh.