The following main challenges and yet unknown biological aspects of POXylation, that need to be addressed to demonstrate the safety as well as potential of POXylation over PEGylation, will be the main objectives to establish the POXylation technology:

- Synthesis of high molar mass PX, ie how to suppress chain transfer reactions;

- Stability and shelf life of POX vs PEG;

- Detailed evaluation of immunological respons of mice to administration of POX and POXylated model proteins;

- Determination of blood circulation times, renal excretion molecular weight limit and potential accumulation of POX and POXylated model proteins in mice;

Close interaction with the industrial user committee will ensure that these investigations will follow (qualified) procedures and methodologies commonly required for FDA approval.