Preparation of Equine Immunoglobulin F(ab′)2 against Smallpox and Evaluation of its Immunoprotective Effect

Smallpox, a severe infectious disease caused by the smallpox virus, causes a death rate as high as 30% within 15-20 days after infection. Therefore, development of anti-Smallpox product as a strategic reserve is urgently needed. We prepared and tested pepsin-digested F(ab′)2 fragments of serum IgG from horses. Transmission electron microscopy indicated that the purified virus showed morphology consistent with VVTT. The titer was above 1.0 × 107 PFU/mL. The purity of the antigen exceeded 90%, according to HPLC. After purification and cleavage, the yield of the purified product F(ab′)2 was approximately 1.3%, its purity exceeded 90%, and the neutralizing antibody titer exceeded 1:3200. F(ab′)2 fragments had good preventive and therapeutic effects in mice at antibody doses of 5.2 mg/mL and 2.6 mg/mL. The viral loads of the drug-treated mice were suppressed to varying degrees, and the higher dose groups (5.2 and 2.6 mg/mL) showed a 2-3 fold lower viral load than that in the control group. A process for producing equine immunoglobulin F(ab′)2 against VVTT was established. The prepared horse anti-smallpox immunoglobulin product had good neutralizing antibody effects on VVTT. The highly purified preparation may serve as a potential candidate for smallpox treatment.