Alpacas produce two types of antibodies: 

(i) conventional antibodies composed of heavy and light chain heterodimers, and

(ii) a class of antibodies consisting solely of heavy chains without light chains, known as heavy-chain antibodies (HcAbs). As shown in Figure 1D, alpaca heavy-chain antibodies lack light chains and are composed of two heavy chains (HCs), each containing one constant domain and one variable domain (VHH). 

The VHH domain is also referred to as single-domain antibody (sdAb). Compared to traditional antibodies, alpaca antibodies offer numerous advantages, including high stability, ease of genetic engineering, low immunogenicity, high specificity, strong affinity, and high expression yields in both eukaryotic and prokaryotic systems. Due to the high sequence similarity between their heavy chain variable regions and human antibody VH domains, they are also more amenable to humanization. Consequently, they are widely applied in current therapeutic antibody research.

Single B Cell Antibody Technology is a relatively recent advancement in antibody generation. KMD Bioscience utilizes this technology to extract lymphocytes from alpaca peripheral blood or lymphoid organs. Specific B cells are then identified and isolated using sorting technologies and subjected to single-cell culture. The specificity of antibodies secreted by individual B cells is assessed using reverse transcription polymerase chain reaction (RT-PCR) with antibody-specific primers. The genes encoding specific antibodies are amplified via PCR, cloned into expression vectors, and expressed in client-specified systems. Purified antibodies are validated for expression using methods such as ELISA. Antibodies obtained by KMD Bioscience using Single B Cell Antibody Technology are of superior quality and exhibit a high success rate.

Figure 1. A, Conventional IgG; B, Fab fragment of conventional antibody; C, Single-chain Fv (scFv) fragment of conventional antibody; D, Heavy-chain antibody or camelid antibody; E, VH domain of camelid antibody or single-domain antibody (sdAb)