DNA impurities in a composition comprising a parvoviral virion

A method of determining whether a composition comprising a parvoviral vector is capable of human use in a clinical treatment, wherein the method comprises the steps of:

• (i) identifying and quantifying an overrepresented nucleic acid impurity in the composition in a method comprising the steps of:
• (a) subjecting the composition to nucleic acid sequencing to obtain at least a thousand random reads of nucleotide sequences;
• (b) comparing, using a processor, the at least a thousand random reads from step (a) with a nucleotide sequence of a biological component used in a process for producing the composition, whereby a match between a random read and the nucleotide sequence of a biological component identifies a nucleic acid impurity;
• (c) determining an average number of reads per parvoviral vector;
• and
• (d) determining a distribution of reads by calculating a number of reads per nucleotide of the identified nucleic acid impurity;
• wherein the identified nucleic acid impurity is identified as the overrepresented nucleic acid impurity when the distribution of reads is not random and the number of reads per nucleotide of the nucleic acid impurity is at least 0.001% the average number of reads per parvoviral vector, and
• (ii) determining the composition as being capable of human use in the clinical treatment if the nucleic acid impurity is at least 10 times less present than a transgene as determined by the relative abundance of the overrepresented nucleic acid impurity.