# Enhancing Antibody-Specific Productivity: Unraveling the Impact of XBP1s Overexpression and Glutamine Availability in SP2/0 Cells

## TL;DR

This study explores how overexpressing XBP1s and managing glutamine levels can boost antibody production in SP2/0 cells while reducing harmful byproducts.

## Contribution

The novel contribution is demonstrating how XBP1s overexpression and glutamine availability impact antibody productivity and bioprocess efficiency in mammalian cells.

## Key findings

- Overexpression of XBP1s increased IgA2m(1) productivity by up to five-fold.
- XBP1s overexpression reduced ammonia and lactate accumulation in cell cultures.
- XBP1s overexpressor cells showed resilience to hydrodynamic stress in serum-free conditions.

## Abstract

Augmentation of glycoprotein synthesis requirements induces endoplasmic reticulum (ER) stress, activating the unfolded protein response (UPR) and triggering unconventional XBP1 splicing. As a result, XBP1s orchestrates the expression of essential genes to reduce stress and restore homeostasis. When this mechanism fails, chronic stress may lead to apoptosis, which is thought to be associated with exceeding a threshold in XBP1s levels. Glycoprotein assembly is also affected by glutamine (Gln) availability, limiting nucleotide sugars (NS), and preventing compliance with the increased demands. In contrast, increased Gln intake synthesizes ammonia as a by-product, potentially reaching toxic levels. IgA2m(1)-producer mouse myeloma cells (SP2/0) were used as the cellular mammalian model. We explored how IgA2m(1)-specific productivity (qIgA2m(1)) is affected by (i) overexpression of human XBP1s (h-XBP1s) levels and (ii) Gln availability, evaluating the kinetic behavior in batch cultures. The study revealed a two and a five-fold increase in qIgA2m(1) when lower and higher levels of XBP1s were expressed, respectively. High h-XBP1s overexpression mitigated not only ammonia but also lactate accumulation. Moreover, XBP1s overexpressor showed resilience to hydrodynamic stress in serum-free environments. These findings suggest a potential application of h-XBP1s overexpression as a feasible and cost-effective strategy for bioprocess scalability.