Transfer factors are a complex group of more than 200 highly polar, hydrophilic, low molecular weight (<12,000 Da) proteins produced in small quantities by lymphoid cells ⁽¹⁾. They can be extracted from human or animal white blood cells, from cloned lymphocytes, or from colostrum, and egg yolk. The parent lymphocyte’s delayed-type hypersensitivity and cell-mediated immunity is passed along to non-immune recipients, and appears to function across species. In animal models, transfer factors were shown to reduce tumor size and increase peripheral blood T-lymphocyte counts  ⁽²¹⁾.

In humans, transfer factors appear to be well tolerated and have shown some efficacy in the treatment of herpes ⁽²⁾, acute infection in children ⁽³⁾, chronic fatigue syndrome ⁽⁴⁾, and Candidiasis ⁽⁵⁾. One study showed effectiveness in increasing white blood cells, CD8 lymphocytes and interleukin 2 levels among patients with HIV ⁽⁶⁾. However, transfer factors were reported ineffective in treating hepatitis ⁽⁷⁾, multiple sclerosis ⁽⁸⁾, extrinsic bronchial asthma ⁽⁹⁾, human warts ⁽¹⁰⁾, juvenile rheumatoid arthritis ⁽²⁸⁾, and acne vulgaris ⁽¹¹⁾.

Transfer factors were also found ineffective against malignant melanoma ⁽¹²⁾, nasopharyngeal carcinoma ⁽¹³⁾, bronchogenic carcinoma ⁽¹⁴⁾, Hodgkin’s disease ⁽¹⁵⁾, osteogenic sarcoma ⁽¹⁶⁾, and mycosis fungoides ⁽¹⁷⁾. However, in a study of children with leukemia, immunization with transfer factors conferred protection against varicella-zoster infection  ⁽²⁰⁾. Other trials have shown increased survival rates among patients with Stage I adenocarcinoma of the lung, ⁽¹⁸⁾ and Stage I cervical cancer ⁽¹⁹⁾.

Overall, there is a paucity of large randomized controlled clinical trials, and a need for further research into the effectiveness of transfer factors.