Viruses & Leukemia

The theory that viruses are to blame for some forms of human cancer, especially leukemia, was strengthened last week by striking evidence gained from experiments with human volunteers. Most notable: the tests gave reason for increased hope that it may be possible to prevent leukemia with a vaccine.

That viruses cause some forms of mouse leukemia has long been accepted, but years of the most exacting research failed to turn up viruses in human victims of a similar disease, acute leukemia. Probably, reasoned Dr. Steven O. Schwartz of Chicago's Hektoen Institute, this was because the virus was somehow modified in the patient's body.

The Choice. The problem was to get the virus in its original state from tissues where the modification did not take place. Dr. Schwartz's choice: the human brain. He took fluid from the brains of patients who had died of leukemia, removed the cells, injected what was left into mice. Many, even in strains that seldom get the disease spontaneously, developed leukemia (TIME, July 27). But rabbits seemed to make antibodies to neutralize the virus. Could the human species do as well?

Yes, Dr. Schwartz told an American Cancer Society meeting in Louisville last week. To get his evidence, he appealed to inmates of Cook County Jail, got 14 volunteers. "Since we are trying to find the answers to human leukemia, we must make tests in man," said Dr. Schwartz. "And we believed there was a minimum of risk to the prisoners." His research teams injected a leukemia victim's fluid into the prisoners' forearm four times, and twice took a pint of their blood.

Then the researchers took batches of identical mice. Into one group they injected the leukemic brain fluid. Virtually all of these developed leukemia. But a second group got an injection of purified serum from the prisoners' blood before the leukemic brain fluid. Only half of these got leukemia. Dr. Schwartz's conclusion: the prisoners, being healthy and not predisposed to leukemia, had reacted the way most normal human beings do, and had made antibodies against the leukemia virus in the brain fluid. These antibodies made their serum work like a crude vaccine, which protected half the mice.

The Hope. Other cancer experts at the meeting were impressed because, if Dr. Schwartz's work can be duplicated and confirmed, it would mark a giant stride against a disease that now kills 12,000 Americans (most of them children) annually. But Dr. Schwartz agreed that the relationship of virus to disease in leukemia must be far more complex than in common illnesses such as smallpox, influenza, measles and polio; for one thing, leukemia is not infectious. Inherited susceptibility is essential, he believes, while hormones and X rays may be important controlling factors. So, he emphasized, a vaccine against human leukemia is still far in the future.

But while some viruses are under indictment as causative factors in certain forms of cancer, others may be helpful in treating the disease. Dr. Bernard Briody of New Jersey's Seton Hall University told the meeting that the cowpox virus (used in smallpox vaccine) kills some cancer cells and retards the growth of mouse cancers. For once, medical scientists did not have to wait years to get evidence of a similar effect in man. By coincidence, Yokohama University's Professor Yoshikuni Noguchi reported simultaneously that he was getting encouraging though temporary results in treating skin cancers (especially on the face and hands) with smallpox vaccine.

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