Neutralizing antibodies to Omicron after the fourth SARS-CoV-2 mRNA vaccine dose in immunocompromised patients highlight the need of additional boosters

Abstract

Introduction: Immunocompromised patients have been shown to have an impaired immune response to COVID-19 vaccines.

Methods: Here we compared the B-cell, T-cell and neutralizing antibody response to WT and Omicron BA.2 SARS-CoV-2 virus after the fourth dose of mRNA COVID-19 vaccines in patients with hematological malignancies (HM, n=71), solid tumors (ST, n=39) and immune-rheumatological (IR, n=25) diseases. The humoral and T-cell responses to SARS-CoV-2 vaccination were analyzed by quantifying the anti-RBD antibodies, their neutralization activity and the IFN-γ released after spike specific stimulation.

Results: We show that the T-cell response is similarly boosted by the fourth dose across the different subgroups, while the antibody response is improved only in patients not receiving B-cell targeted therapies, independent on the pathology. However, 9% of patients with anti-RBD antibodies did not have neutralizing antibodies to either virus variants, while an additional 5.7% did not have neutralizing antibodies to Omicron BA.2, making these patients particularly vulnerable to SARS-CoV-2 infection. The increment of neutralizing antibodies was very similar towards Omicron BA.2 and WT virus after the third or fourth dose of vaccine, suggesting that there is no preferential skewing towards either virus variant with the booster dose. The only limited step is the amount of antibodies that are elicited after vaccination, thus increasing the probability of developing neutralizing antibodies to both variants of virus.

Discussion: These data support the recommendation of additional booster doses in frail patients to enhance the development of a B-cell response directed against Omicron and/or to enhance the T-cell response in patients treated with anti-CD20.

Keywords: Omicron neutralization; SARS-CoV-2 mRNA vaccine; T cell response; cross immunity; humoral response; immunocompromised patients.

Figure 1

Humoral and T-cell response to the fourth dose of mRNA vaccine in fragile patients. (A) SARS-CoV-2 specific anti-RBD antibodies (Abs) were measured in sera samples of HM (green dots), IR (blue dots) and ST (red dots) patients before (pre) and after (post) the fourth dose of mRNA vaccine. The level of anti-RBD Abs was expressed as BAU/mL. HM-pre median= 274.8 BAU/mL (IQR 5.2–1357 BAU/mL); HM-post median=1624.0 BAU/mL (IQR 10.7-7269). IR-pre median= 7.6 BAU/mL (IQR 1.0-128.3 BAU/mL); IR-post median= 30.5 (IQR 2.2-1458 BAU/mL). ST-pre median= 1546.0 BAU/ml (810.4-4389 BAU/mL); ST-post median= 7632 (3023-11360 BAU/ml). The dashed line indicates the cut-off value (7.1 BAU/mL). Differences between anti-RBD Abs titre before and after the fourth dose within the same group were evaluated by Wilcoxon paired test, while differences across groups were evaluated by Kruskal-Wallis. ****P<0.0001; ***P<0.001. (B) T-cell response were measured in HM (green dots), IR (blue dots) and ST (red dots) patients before (pre) and after (post) the fourth dose of mRNA vaccine. Spike-specific T-cell response was measured after stimulation of whole blood with specific peptides and was expressed as pg/mL of IFN-γ and values 0.12 pg/mL are considered positive. HM-pre median= 44.0 pg/mL (IQR 3.1-185.3 pg/mL); HM-post median=112.6 pg/mL (IQR 14.4-350.9 pg/mL). IR-pre median= 74.8 pg/mL (IQR 28.1-233.0 pg/mL); IR-post median= 175.5 pg/mL (IQR 60.1-595.2 pg/mL). ST-pre median= 48.9 pg/mL (11.9-167.3 pg/mL); ST-post median= 176.0 pg/mL (60.5-495 pg/mL). The dashed line indicates the cut-off value (12 pg/mL). Differences between IFN-γ level before and after the fourth dose within the same group were evaluated by Wilcoxon paired test, while differences across groups were evaluated by Kruskal-Wallis. ****P<0.0001; ***P<0.001. HM, hematological malignancies; IR, immune-rheumatological diseases; ST, solid tumors. **P<0.01; *P<0.05.

Figure 2

Neutralization response to the fourth dose of mRNA vaccine in fragile patients (A) The levels of neutralizing antibodies were quantified by microneutralization assay (MNA₉₀) against Omicron BA.2 in HM (green dots), IR (blue dots) and ST (red dots) before (pre) and after (post) the fourth dose of mRNA vaccine. The MNA₉₀ was measured only in patients showing a positive anti-RBD response. The results were expressed as reciprocal of dilution and values >5 are considered positive. HM-pre median= 10 reciprocal of dilution (IQR 5-40); HM-post median=80 reciprocal of dilution (IQR 10-320). IR-pre median= 5 reciprocal of dilution (IQR 5-30); IR-post median= 15 reciprocal of dilution (IQR 5-40). ST-pre median= 20 reciprocal of dilution (IQR 10-80); ST-post median= 160 reciprocal of dilution (IQR 50-320). Differences between MNA₉₀ titre before and after the fourth dose within the same group were evaluated by Wilcoxon paired test, while differences across groups were evaluated by Kruskal-Wallis. ****P<0.0001; **P<0.01. (B) The levels of neutralizing antibodies against wild-type (WT) and BA-2 Omicron (BA.2) strains after the fourth dose of mRNA vaccine were compared in HM (green dots), IR (blue dots) and ST (red dots). The results were expressed as reciprocal of dilution and values >5 are considered positive. HM-WT median=1280 reciprocal of dilution (IQR 80-1280); HM-BA.2 median=80 reciprocal of dilution (IQR 10-320). IR-WT median= 80 reciprocal of dilution (IQR 5-640); IR-BA.2 median= 10 reciprocal of dilution (IQR 5-40). ST-WT median= 1280 reciprocal of dilution (IQR 640-1280); ST-BA.2 median= 160 reciprocal of dilution (IQR 40-320). Differences were evaluated by Kruskal-Wallis test. ****P<0.0001; ** P<0.01. (C) The levels of neutralizing antibodies against wild-type (WT) and BA-2 Omicron (BA.2) strains after 10-20 days from the third (post-3) and fourth (post-4) dose of mRNA vaccine were compared in a subgroup of patients (n=21). The results were expressed as reciprocal of dilution and values >5 are considered positive. WT-post-3 median=160 reciprocal of dilution (IQR 5-520); WT-post-4 median= 320 reciprocal of dilution (IQR: 5-1280). BA.2-post-3 median= 15 reciprocal of dilution (IQR 5-80); BA.2-post-4 median= 40 (IQR 5-240). Differences between neutralization titre against WT and BA.2 after the third and fourth dose evaluated by Wilcoxon paired test ***P<0.001. HM, hematological malignancies; IR, immune-rheumatological diseases; ST, solid tumors.

Figure 3

Impact of different treatments on humoral and T-cell response (A) SARS-CoV-2 specific anti-RBD Abs and T cell response before (pre) and after (post) the fourth dose of mRNA vaccine were compared in HM patients receiving different treatments: Rituximab (RTX), hematopoietic stem cell transplantation (HSCT), Chemotherapy (ChTX), JAK inhibitors (JAK) or others. (B) SARS-CoV-2 specific anti-RBD Abs and T cell response before (pre) and after (post) the fourth dose were compared in IR patients receiving different treatments: Rituximab (RTX) and other (methotrexate, mycophenolate mofetil, and azathioprine). (C) SARS-CoV-2 specific anti-RBD Abs and T cell response before (pre) and after (post) the fourth dose of mRNA vaccine were compared in ST patients receiving different treatments: Chemotherapy (ChTX), Immunotherapy (ImmTX) and Target therapy (TarTX). The median and IQR are described in Supplementary material. Differences between anti-RBD or T cells response level before and after vaccination within the same group was evaluated by Wilcoxon paired test, while differences across groups were evaluated by Kruskal-Wallis. ****P<0.0001, ***P<0.001, **P<0.01, *P<0.05. HM, hematological malignancies; IR, immune-rheumatological diseases; ST, solid tumors.