Experimental and modeling study of a membrane filtration process using ceramic membranes to increase retroviral pseudotype vector titer

The ability of commercial ceramic asymmetric ultrafiltration membranes with a cut-off of 20 kDa to purify retroviral pseudotype vectors derived from the murine leukemia virus (MLV) carrying the HIV-1 envelop protein MLV (HIV-1) was studied. To optimize the filtration process a mathematical model of batch wise vector purification was set up. Seven hundred and forty-five to 1794 ml batches of supernatant containing a maximum of 3.2×105 colony forming units per ml (cfu ml−1) was produced in a 200 ml fixed bed reactor. By cross flow filtration the vector concentration was increased 10-fold with an average recovery of 84.5 ± 4.5% of the initial infective capacity. Furthermore membrane layer formation and temperature dependent decay of transduction competent vector particles (decay) was included in the mathematical model. A maximal end point titer of 4.1×106 cfu ml−1 was predicted by the model and confirmed reasonably well by experimental data. The transmembrane flow of batch filtration was predicted by solving a set of related differential equations. Our modeling allows scale-up of the process and prediction of process performance including specific issues such as vector degradation.