Cross clade prophylactic and therapeutic efficacy of polyvalent equine immunoglobulin F(ab')2 against highly pathogenic avian influenza H5N1 in mice.

Highly pathogenic avian influenza H5N1 virus (HPAI H5N1) has the potential to cause a new pandemic, which may lead to disasters in the world. However, we cannot predict the HPAI H5N1 strain that might cause the pandemic. Therefore, broad-spectrum prophylactic or therapeutic preparations for containment of a possible future pandemic are urgently needed. Polyvalent equine immunoglobulin F(ab')2 may be a promising candidate.We prepared four pepsin digested immunoglobulin F(ab')2 from the horses immunized with purified VNH5N1-Puerto Rico/8/34 (PR8)/CDC-RG (VNRG, Clade 1), A/Indonesia/05/2005(H5N1)-PR8-IBCDC-RG2 (INRG, Clade 2.1), and A/Anhui/01/2005(H5N1)-PR8-IBCDC-RG5 (AHRG, Clade 2.3.4) and PBS (negative control), respectively. The protective effect of the monovalent or polyvalent F(ab')2 against A/Ostrich/SZ/097/04 (clade 0) infection was determined by cytopathic effect (CPE) in cultured Madin-Darby canine kidney (MDCK) cells. The prophylactic and therapeutic efficacy of the polyvalent F(ab')2 was further evaluated by observing survival, weight loss and viral load when the polyvalent F(ab')2 was introduced into mice one day prior to-, three days post-lethal challenge with A/Ostrich/SZ/097/04.The half neutralization doses (ND50) of purified monovalent equine F(ab')2 prepared by the VNRG, INRG or AHRG-immunized horses and polyvalent one against A/Ostrich/SZ/097/04 were 320, 1280, 1280 and 2560 in cultured MDCK cells, respectively. 10 μg polyvalent F(ab')2 could completely protect mice infected with 100 half lethal doses (LD50) of A/Ostrich/SZ/097/04 in preventive settings. In therapeutic settings, even when injected three days post lethal infection, mice were still completely protected, although 200 μg of polyvalent F(ab')2 was required.Our work has provided experimental supports for testing the broad-spectrum protective efficacy of polyvalent equine immunoglobulin F(ab')2 for the future large trials.