The Gibco Diploid Serum-Reduced Medium (SRM) system is designed to support vaccine manufacture under serum-reduced or serum-free conditions for cell types traditionally cultured in classical media with 10% serum. With this system, human diploid cells, such as MRC-5, Wi38, and KMB17, can be grown with just 1–2% serum. Additionally, it supports growth of chicken embryo fibroblasts under serum-free conditions. Virus production can then be conducted under serum-free conditions without the addition of albumin or other supplements.

The Diploid SRM system is composed of two different kits:
1. Diploid Growth Serum-Reduced Medium (SRM) kit: A basal medium and 100X growth supplement designed for cell expansion
2. Diploid Production Serum-Free Medium (SFM) kit (this page): A basal medium and 100X production supplement designed for virus production

Human cells have traditionally been used to manufacture a variety of vaccines, such as the varicella zoster, polio, smallpox, hepatitis A, measles, mumps, and rubella vaccines. Traditionally, the only way to culture these cells has been to use classical media with 10% serum for growth and 1–5% human albumin (human sourced or recombinant) for virus production. These are two of the highest cost components in vaccine production. The Diploid SRM system helps reduce or eliminate both components while maintaining high virus titers.

Cost savings
Reduction or elimination of serum can significantly reduce cost for a vaccine manufacturing process. Premium FBS is expensive with high price volatility. Given the typical cost pressures on vaccine production, both economic drivers make vaccine manufacturing to a target price extremely challenging. Diploid Growth SRM reduces the impact of this volatility in price and offers a level of cost consistency not available with processes that use serum in high volumes.

In addition, serum requires frozen storage. A 10% serum concentration in growth media can result in high frozen storage requirements for a vaccine process. A process requiring 1,000 L of growth medium would require the frozen storage of 100 L of serum. The Diploid Growth SRM kit comes with a 100X frozen supplement, enabling an 80% reduction in frozen storage requirements. 1,000 L of Diploid Growth SRM would only need 20 L of frozen storage: 10 L for FBS and 10 L for the 100X supplement.

Albumin is commonly added to virus production media. With the Diploid Production SFM, viruses can be produced at comparable titers without any additional supplementation.

No adaptation required
The Diploid SRM system was developed with existing cell banks in mind. Transitioning a vaccine process to a new medium can be challenging due to the need to adapt the cells to the new medium. For human cells such as MRC-5, there is the added risk of reaching the Hayflick limit due to the added passages necessary during cell adaptation and subsequent re-banking of the cells. The transition to the Diploid SRM system does not require adaptation or re-banking of cells when using the Diploid Growth SRM kit. Existing cGMP cells banked with serum may be thawed directly in Diploid Growth SRM supplemented with 1% FBS, allowing a simple transition to this medium.

Mitigate serum supply risk
Obtaining a steady supply of serum can be challenging, especially if the serum required is from a BSE/TSE safe region such as New Zealand or Australia. Serum supply can fluctuate based on several environmental (drought, cattle disease) and economic (feed cost, dairy pricing) factors. With Diploid Growth SRM this dependence is substantially reduced due to the reduced serum requirements.