has proved particularly effective in patients with acute leukemias and other blood cancers by contrast those like mr olson with chronic lymphocytic leukemia also known as cll have seen less success among those with that cancer about a third to a fifth go into remission with car t therapy but many whose cancers disappear later relapsethe question is not only why some patients relapse or are resistant to therapy but why are some patients cured said dr john f dipersio chief of the division of oncology at washington university in st louis who was not involved in the studythe car t treatment has also caused serious side effects in some patients like high fevers comas dangerously low blood pressure and even death although in most patients the alarming symptoms resolve it has not yet worked in people with the solid tumors found in conditions like breast and prostate cancerjust as strange as the inability of car t to help most cancer patients is the fate of those modified t cells in the cured patientsthe genetic modification involved a subset of t cells known as cd8 cells which are assumed to be the ones that actually kill the cancer they are the assassins of the immune systembut assassins need helpers and for the cd8 cells the helpers are another group of t cells known as cd4 cellsat first the cd8 cells seemed to be acting exactly as was hoped in dr junes study the modified cd8 t cells almost immediately killed between 3 and 7 pounds of cancer cells in the bodies of mr olson and the first patient in the study william ludwig who was also cured of his cancer but died last year from covid19after the cd8 cells did their job they remained in the blood but unexpectedly they turned into cd4 cells and when the penn investigators removed cd4 cells from the blood of mr ludwig and mr olson they saw that those cells could kill b cells in the laboratory the cd4 cells had turned into assassins or dr dipersio noted at least guardians that can keep the tumor cells at bay and undetectable in the patient for yearscould the cd4 cells remain in the blood with no cancer cells to kill or were they there because the leukemia was not really gone but instead kept trying to return only to be attacked by cd4 cellswe cant find any leukemia cells in doug dr june said but he added perhaps they are still there in tiny quantities and emerging only to be knocked back by cd4 cells like whackamole he saidhe suspects though that the cd4 cells are more like guardsthe leukemia is gone but they stay on the job he saidwhatever the mechanism dr porter said the result is beyond my wildest imaginationoncologists dont use words like cure lightly or easily or frankly very often he said i guarantee that its not being used lightly the patients we treated had far advanced disease he noted adding