Major Risks of Secondary Immunization in Alpacas: A Special Topic on Nanobody Development

In addition to being able to produce different types of antibodies, the differences between alpacas and mice, rabbits include higher costs for transportation, breeding, and immunization operations. This creates a certain degree of contradiction with the market demand for nanobodies. Therefore, the practice of conducting secondary immunization on alpacas in the market has gradually emerged. However, this seemingly cost-saving approach to antibody development actually brings significant risks and introduces unlimited uncertainty for the downstream application development of nanobodies. This article will elaborate on the importance of "zero immunization background", that is, the disadvantages of secondary or multiple immunizations of alpacas.

ONE: Immune interference

       The immune system of immunized alpacas, due to previous exposure to other antigens, contains a large number of VHH genes targeting the previously encountered antigens in their B cell libraries. When using new antigens for immunization, these pre-existing memory B cells will proliferate preferentially, which may lead to insufficient coverage of antigenic epitopes and the risk of cross-reactive interference.

Epitope preference shift 
Previous immunization may induce immune tolerance or excessive competition in alpacas for certain epitopes. For example, in the study of the spike protein of the novel coronavirus, the antibodies produced in immunized alpacas focused on non-critical epitopes (such as the S2 subunit), while un-immunized alpacas were more likely to target neutralizing epitopes (such as the RBD region). 
Cross-reactivity interference 
Pre-stored antibodies may non-specifically bind to new antigens. For instance, antibodies targeting GPCR targets may bind to previous antigens due to structural similarity, resulting in false positive screening results. Additional verification through epitope localization or competitive experiments is required.

      In fact, the biggest problem with immune interference stems from the lack of knowledge about previous antigens. Because some clients, when seeking immune services from providers, would omit the names, types, and labels of the antigens, it becomes difficult to determine whether the new antigens are consistent or conflicting with the old ones during the second immunization process. This can lead to immune failure, insufficient affinity, or even non-specificity, among other outcomes.

Two: Immune Library Contamination

    The problem of immune interference caused by insufficient antibody binding ability due to previous immunization of alpacas will further lead to contamination of the immune library by previous antigens. This will result in a decrease in the proportion of target antibodies and a significant reduction in the screening efficiency.、The risk of a significant reduction in screening efficiency.

The proportion of the target antibody has decreased. 
In the phage display library, non-target antibodies (such as VHHs targeting previously encountered antigens) may occupy more than 50% of the library capacity; 
The screening efficiency has decreased. 
A large number of non-specific antibodies need to be excluded through multiple rounds of "pre-clearing" or additional screening steps, resulting in a 2-3 times increase in workload and the possibility of missing low-abundance but high-affinity antibodies.

THREE: Limited antibody diversity

       已免疫羊驼的B细胞经历多次克隆选择后，其VHH基因库的After multiple rounds of clonal selection in the B cells of immunized alpacas, the diversity of their VHH gene pool significantly decreased. 
Homologization of the framework region (FR) 
Previous immunization may lead to convergent evolution of the FR region genes, thereby limiting the diversity of antibody structures; 
Conservation of the complementarity determining region (CDR) 
The length of CDR3 may be shortened (averaging a reduction of 2-3 amino acids), which weakens the ability to recognize complex epitopes. And the shortening of CDR3 length significantly reduces the advantages of nanobodies.

FOUR: The cost of humanization modification and the difficulty in achieving affinity maturation have increased.

      The VHH sequences of nanobodies that have been immunized in alpacas may possess more non-humanized characteristics. 
Residual immunogenicity hotspots 
Previous antigen stimulation may cause more camel-specific epitopes to be exposed on the antibody surface. This needs to be eliminated through site-directed mutagenesis or CDR transplantation, and the modification process will increase by 30% to 50%. 
Glycosylation site interference 
Some already immunized antibodies retain glycosylation modifications due to previous antigen requirements (such as the Asn-X-Ser/Thr motif). To accommodate this, the expression system needs to be changed (from prokaryotic to eukaryotic), resulting in a production cost increase of more than twice. 
Pre-stored mutation interference 
The VHH genes of immunized antibodies may accumulate random mutations, such as non-functional mutations (e.g. Pro→Leu) in the FR2 region, and these need to be restored to stability through reverse mutations. 
Enhancing affinity through space compression 
Previous immunization may have already caused the antibody affinity (KD value) to approach the plateau (such as 10^-8 M). Further optimization requires the introduction of high-risk mutations, such as the insertion of CDRs that disrupt structural stability.

FIVE: Functional design limitations and uncontrollable immunogenicity

       由于已免疫羊驼体内的纳米抗体可能携带既往免疫抗原相关的糖基化修饰，进而导致其Because the nanobodies already present in the immune-sheep's body may carry glycosylation modifications related to previous immune antigens, this can lead to an increase in the rigidity of the antibody structure, an increased risk of epitope conflicts, and an uncontrollable enhancement of immunogenicity. 
Increased structural rigidity 
The conformation of the immune antibodies may become fixed due to the previous binding requirements, thereby limiting their synergistic effect with fusion proteins (such as IL-2 conjugates). 
Epitope conflict risk 
The engineering modification involves the design of bispecific antibodies. The epitope binding patterns of previous antibodies may cause spatial obstruction when interacting with the new target. 
Immune response is uncontrollable. 
Due to the glycosylation modification of the previous immunogen, the frequency of N-glycosylation sites in the VHH fragment is three times that of the non-immune group. This modification will affect the pharmacokinetic properties of the antibody and even trigger an immune response.

SIX: Intellectual property risks and overall cost increases

       Using immunized alpacas may lead to patent disputes. According to statistics, approximately 41% of the publicly disclosed alpaca-related antibody patents worldwide involve specific antigen immunization schemes. If relevant antibodies are developed using immunized alpacas, there may be legal risks due to falling within the protection scope of existing patents. 
Due to potential immune failure or low antibody titers, using immunized alpacas may increase the overall research and development costs by 30% to 60%, mainly manifested in the following aspects. 

Summary

 Therefore, using secondary immunization of alpacas for antibody development may seem to save costs, but the potential risks and the subsequent increase in costs may be incalculable. Whether it is library contamination, epitope shift, or obstacles in antibody engineering, all these issues will cause the entire research and development process to fall into an inefficient and resource-intensive predicament. In the era of precision medicine, choosing alpacas with "zero immunization background" to avoid potential problems in antibody drug development from the very beginning is not only the optimal solution in terms of technology and investment, but also the core guarantee for the success rate of clinical transformation of antibody drugs. 
From the very beginning of its establishment, Nabao Life has built a camelpus experimental and breeding base that meets the standards for laboratory animal facilities, and it is located in both Wuhan Zoling and Huanggang Tongfeng. The camels are all directly purchased from South American countries such as Peru, and a traceability system is in place. After the camels in the experimental base complete the immunization service, they are sent to the breeding base, where they are isolated from the experimental camels to avoid confusion in cross-management. Nabao can provide a complete camel immunization service with "zero immunization guarantee" for research institutions and antibody drug development enterprises, ensuring that the basic interests of the clients are not infringed upon, guaranteeing the success rate of antibody development from the source, and saving time and economic costs for downstream antibody identification. 
Nabo Life currently possesses a complete chain technology platform covering antibody development, discovery, and engineering. This platform includes screening platforms such as phage display, Escherichia coli display, and mammalian cell display, as well as membrane protein/mRNA-LNP preparation and immunization platforms. Through the cross-complementation of multiple platforms, it provides flexible antibody discovery and modification services for pharmaceutical companies and research institutions, assisting in the development of drugs and reagents.

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   Nabo Life focuses on the development, modification and application of nanobodies. It has a breeding base for alpacas that meets the standards for laboratory animals and an independent laboratory base. It is committed to building an integrated experimental public service platform for production, education and research. We hope to provide more professional, cost-effective and more reliable experimental services for a wide range of biological research institutions, pharmaceutical research and development enterprises and innovation teams. 
For more service details, please follow the Nabo Life official account or call the official hotline 400-822-9180 for consultation!