The effects of 13‐cis‐retinoic acid and beta‐carotene on cellular immunity in humans

Deficiency of vitamin A and/or its precursors has been associated with increased cancer risk in animals and humans. Therapeutic trials of vitamin A and related compounds have demonstrated activity in several cancerous and precancerous conditions. The authors measured the effects of a retinoid, 13‐cis‐retinoic acid, and a carotenoid, beta‐carotene, on the human immune system in vivo in conjunction with their use in ongoing clinical trials. Immune cell subpopulations were analyzed by quantifying the expression of markers using flow cytometric study. Both compounds produced significant effects on immune cell populations. 13‐cis‐Retinoic acid resulted in an increase in the percentage of peripheral blood lymphoid cells expressing surface markers for T‐helper cells with only minimal effect on natural killer cell marker expression. In contrast, beta‐carotene produced an increase in the percentage of cells expressing natural killer cell markers with smaller effect on T‐helper markers. Modest increases in the percentage of cells expressing Ia antigen, transferrin, and interleukin‐2 receptors were produced by both drugs. These results suggest that retinoids and carotenoids can produce major changes in immune cellular marker expression in vivo in humans at doses relevant to their potential clinical use.