GMHC Treatment Issues - Vol. 9, No. 12 - December 1995
Dennis Sawyer

Products arising in such an unregulated environment frequently are rushed into human use without the proper lab and animal studies to gather preliminary safety and efficacy information. Cytolin is no exception.

The Rationale for Cytolin

Cytolin is the trade name for an experimental therapy under development by CytoDyn of New Mexico, Inc., a start-up biotech firm led by a physicist named Al Allen. It reportedly consists of a specific antibody derived from mice that is infused over twenty minutes, with repeat administration every four weeks. The mouse antibodies that make up Cytolin do not recognize or bind to HIV at all. They only recognize and bind to a specific protein, known as S6F1, found on the surface of a subgroup of CD8 cells that help control viral infections. In theory, Cytolin should not interfere with the critical functions provided by other immune cells that lack the S6F1 surface proteins.

According to a paper published in 19901 by Joyce Zarling and research conducted by Al Allen,2 HIV over-stimulates circulating S6F1-marked CD8 cells, causing them to "behave inappropriately." The CD8 cells destroy essential CD4 cells whether those cells are infected with HIV or not, "eventually facilitating immune system collapse."

CytoDyn also has stated that "various" (uncited) studies have pointed out the detrimental effects of S6F1-marked cells on immune function according to two additional scenarios: 1) The S6F1 cells might themselves be providing a pathway needed by HIV to replicate, or 2) the S6F1 cells might be interfering with the body's mechanism (the monocyte-macrophages) to clear infected cells.

Risks and Benefits

Thus far, a few hundred individuals have received Cytolin with their ongoing treatment regimens under the supervision of their primary care providers.

As expected with the introduction into the body of a non-human protein-based substance like mouse antibodies, administration of Cytolin causes serum and protein sickness. Some patients experienced mild flu-like serum sickness reactions, such as low-grade fever, swollen lymph nodes, and body aches within hours of Cytolin injection. Temporary mood changes, such as depression, irritability and anxiety lasting for several days were also reported. The occurrence of these side effects, largely attributable to cytokine release, can be minimized by administering ibuprofen such as Advil or Motrin to the patients just prior to infusion and for twelve hours thereafter.

Several patients have also developed much more serious allergic or anaphylactic reactions. Taking Benadryl prior to Cytolin may reduce these possibly fatal reactions, but this has not been established.

Critics also have warned that Cytolin can neutralize the critical role that CD8 cells possessing S6F1 play in killing cancerous or virus-infected cells. Cytolin may promote the spread of lymphomas or Epstein-Barr virus, for example.

Proponents of Cytolin have claimed that both increases in CD4 counts and improvements of immune responses, as measured by delayed-type hypersensitivity skin tests, have occurred in treated patients with early HIV disease. Apparent resolutions of molluscum contagiosum, a skin condition associated with HIV infection, were seen in some Cytolin recipients. But one doctor reports that of 19 patients on Cytolin, 13 experienced a "clinically significant" event.

It is hard to judge the importance of such anecdotal evidence. The medical experience of individuals on Cytolin is not recorded in a precise or uniform manner. Those who drop therapy because they are doing poorly tend to get lost from the record entirely. Also, Cytolin's proponents do not weigh the effects of concomitant therapies taken for HIV and opportunistic infections.

Now, Victor Beer, M.D., of Los Angeles will conduct an initial dose-ranging trial to gauge the pharmacodynamics and safety of Cytolin in 16 healthy HIV-positive people with CD4 counts between 200 and 500 and no prior or stable (at least two months) antiretroviral therapy. Endpoints include viral load and CD4 counts. Participants will receive either placebo, "the current dose of Cytolin," two times the current dose or five times the current dose. Larger trials are envisioned for next summer.

While awaiting some reliable data, those eager to try this agent should remember Cytolin's risks as well as its promise.

1 Zarling, JM et al. Journal of Immunology. Apr 15 1990; 144(8):2992-8.

2 Company literature. A report on the science study of A.D. Allen at al. Lay Language Summary.

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