Typhim vi immunization assists to discriminate primary antibody responses in hematological malignancies.

Assessment of specific antibody (Ab) production to polysaccharide antigens is clinically relevant, identifying patients at risk for infection by encapsulated bacteria and thus enabling a more rigorous selection of patients that can benefit of immunoglobulin replacement therapy. Classically, the gold-standard test is the measurement of antibody production to pure polysaccharide pneumococcal (PPV) immunization. Several factors, including introduction of conjugate vaccination schedule, serotyping analysis, high baseline Ab levels, have hindered the evaluation of polysaccharide antigens. This is even more difficult in secondary immunodeficiencies (SID), where patients can show secondary responses despite lack of primary antibody responses and present with recurrent or severe infections. Assessment of specific Ab production to pure Salmonella typhi Vi polysaccharide (TV) immunization has been proposed as a complementary test to PPV, given its low seroprevalence. To set the optimal cut-off value for PPV and TV response in SID, we tested different biostatistical methodologies, including ROC analysis, Youden index, Union index and Closest-topleft in a cohort of 42 SID patients and 24 healthy controls. The statistically chosen cut-offs value pre-post TV Ab ratio was ≥5, (sensitivity of 90%, specificity of 100%) and a postvaccination TV concentration of 28.5 U/mL (sensitivity of 90%, specificity of 95%), showing relevant clinical correlate.

Evaluation of Polysaccharide Typhim Vi Antibody Response as a predictor of Humoral Immunodeficiency in Haematological Malignancies.

An increasing healthcare challenge in the management of haematological malignancy (HM) is secondary immunodeficiency. From January 2019, the EMA included the evaluation of specific antibody (Ab) responses to better select patients for immunoglobulin replacement therapy (IgRT). We evaluated Ab responses to pneumococcal and Salmonella typhi pure polysaccharide immunization in a cohort of 42 HM patients and 24 healthy-controls. Pre-post specific Ab concentrations were measured by ELISA at 4 weeks. Globally, significantly lower Typhim Vi (TV) seroprevalence (9%) compared to 23-valent pneumococcal polysaccharide vaccine (PPV) (76%) (p <0.001) was observed. TV non responders (88%) were higher than PPV non responders (62%) (p <0.0001) and correlated better to infectious history. By ROC analysis, pre-post 5-fold TV increase was the best cut-off to discriminate HM with recurrent infections and controls (sensitivity 91%, specificity 100%). Despite the small sample cohort, our results suggest that specific anti-S typhi Ab response is a useful complementary assay in the diagnosis and management decision of SID to HM.