CH2 Domain Mutations Technology

Mutant Fc domains interact with key sites of Fcγ receptors and C1q, which can reduce or remove their binding capacity. Specific mutagenesis techniques allow for the determination of the region in which C1q binds to the antibody, including the hinge region and the CH2 domain above the Fc domain. CH2 domain mutation technology selectively regulates the interaction of antibodies with FcgR and C1q expressed on the surface of immune cells by mutating the CH2 domain in the Fc region of the antibody, thereby enhancing efficacy.

Background

Studies have shown that initiation of antiretroviral therapy (ART) is advantageous during acute HIV infection (AHI). These include reducing the size of the HIV reservoir and preserving a homogeneous viral reservoir (no escape mutations). However, little is known about the characterization of HIV antibody production with early treatment.

Seroconversion occurs at the peak of AHI stage 3 (S3). Detectable free antibodies that recognize gp41 in the blood and can cross-react with the gut microbiota, showing relatively high somatic mutations. Antibodies that recognize gp120 appear later, initially exhibiting non-neutralizing activity. The study found that the early antibody response to HIV did not significantly affect VL, and the escape mutation of antibody selection was not discovered until autologous neutralizing antibodies appeared months after infection. While other antibody functions, such as antibody-dependent cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP)-mediated inactivation, can provide some protection prior to neutralization.

Main Method

In this study, all mAbs used in the luciferase ADCC assay were IgG1 constant region generation from alanine substitutes (S298A, E333A, K334A). This region is designed to enhance binding to Fc-γ receptor IIIa (FcR3A).

Research Results

Period of production of HIV-specific antibodies with ADCC function.
Fig.1 Period of production of HIV-specific antibodies with ADCC function.1,2	CXCL13 level in plasma is a biomarker of GC activity. CXCL13 level was measured and showed higher in the later phase of AHI infection (Fig.1 B). The gp41-specific and gp120-specific antibody responses in plasma during the S4/5 phase of infection were significantly higher than the early phase of AHI (Fig.1 C). In addition, patients in the S4/5 phase had significantly higher ADCC titers against CRF01_AE infection targets than in the early phase of AHI (Fig.1 E). The above data suggested that HIV-specific antibodies with ADCC function are not produced until S4/5 of AHI.
Period of treatment for AHI that produces Ab after the start of ART.
Fig.2 Period of treatment for AHI that produces Ab after the start of ART.1,2	Due to the low viral load at the onset of ART, participants treated during the S1 period of infection had a significantly shorter time to first undetectable VL than those in S3 and S4/5 (Fig.2 A). Fig.2 B showed that there is no significant difference in VL AUC between participants initiating treatment in S2, S3, and S4/5 of AHI. The above data indicated that the virus is suppressed after initiation of antiretroviral therapy.
Ab levels increased in the first 6 months of ART.
Fig.3 Ab levels increased in the first 6 months of ART.1,2	The results showed only a modest correlation between VL AUC and all Ab measurements at 48 weeks (Fig.3 A). In addition, Fig.3 B showed that VL AUC is significantly correlated with Env-specific antibody levels and ADCP, but not with ADCC. The above data suggested that viral antigen load (VL AUC) after ART may be related to HIV-specific binding antibody levels, and that other factors must contribute to the ADCC response during AHI.
Period of increased cross-branched ADCC antibody response.
Fig.4 Period of increased cross-branched ADCC antibody response.1,2	The results showed that the number of participants who generated a cross-clade ADCC response in the early stages of AHI was small, and conversely more than 50% in the S4/5 phase (Figure 4A). Participants treated in the AHI S4/5 phase experienced a significant increase in the magnitude of the C-specific ADCC response after 48 weeks (Figure 4B). In addition, there was a correlation between C-specific ADCC responses at weeks 24 and 48 (Figure 4C). Figure 4F shows some degree of correlation between CRF01_AE-specific and branch-C-specific ADCC responses at week 48. The above data suggested that participants who start treatment in the AHI S4/5 phase have a greater ability to produce ADCC antibodies cross-clade between 24 and 48 weeks of suppressive therapy.

Advantages

1) Enhanced activity to promote immune response: selectively promotes binding to FcgRIIIa and/or FcgRIIa receptors, thereby mediating ADCC and ADCP effects;

2) Reduced activity to inhibit autoimmunity: selectively promote binding to FcgRIIb receptors, reduce the immune response of B cells, and thus inhibit antibody-mediated autoimmunity;

3) Elimination of cytotoxicity: Elimination of binding to all FcgRs and C1q, avoiding effector cell-mediated cytotoxicity.

References

1. Mitchell, Julie L et al. "Anti-HIV antibody development up to 1 year after antiretroviral therapy initiation in acute HIV infection." The Journal of Clinical Investigation. 132,1 (2022): e150937.
2. Distributed under Open Access license CC BY 4.0, without modification.