Obviousness

Obviousness Analysis under 35 U.S.C. § 103 for US Patent 9051542

To determine if the claims of US patent 9051542 are obvious under 35 U.S.C. § 103, we must consider whether the differences between the claimed invention and the prior art would have been obvious to a person having ordinary skill in the art (POSA) at the time of the invention (priority date: June 1, 2004). The primary independent claim is Claim 1, which describes a composition for storing purified, recombinant AAV vector particles.

Independent Claim 1:

A composition for the storage of purified, recombinant adeno-associated virus (AAV) vector particles, comprising:

• purified, recombinant AAV vector particles at a concentration exceeding 1×10^13 vg/ml up to 6.4×10^13 vg/ml;
• a pH buffer, wherein the pH of the composition is between 7.5 and 8.0; and
• excipients comprising one or more multivalent ions selected from the group consisting of citrate, sulfate, magnesium, and phosphate; wherein the ionic strength of the composition is greater than 200 mM, and wherein the purified AAV vector particles are stored in the composition without significant aggregation.

Prior Art and Its Disclosures:

The patent itself acknowledges several relevant pieces of prior art and existing knowledge:

1. Problem of AAV Aggregation: Huang, J. et al. (2000) reported that AAV vectors undergo concentration-dependent aggregation. Xie, Q. et al. (2004) similarly reported that at concentrations exceeding 0.1 mg/mL, AAV2 vectors require "elevated concentrations of salt to prevent aggregation." The patent states that aggregation occurs at particle concentrations exceeding 10^13 particles/mL in commonly used neutral-buffered solutions. This establishes the known problem and the need for solutions to prevent aggregation, especially at high concentrations.
2. Effect of Salt Concentration: It was generally known that high salt concentrations, such as those found in CsCl gradients used for purification, could maintain AAV2 solubility. Xie et al. (2004) explicitly taught the need for "elevated concentrations of salt" to prevent aggregation.
3. Importance of Isotonicity: The patent highlights that "optimal formulations for pre-clinical and clinical studies should be close to isotonic (280-400 mOsm), especially for in vivo administration of vector to sites where dilution of hypertonic solutions may be slow." This indicates a known desire in the field for isotonic formulations.
4. Common Multivalent Excipients: The patent states that "salts of sulfate, citrate, and phosphate that are commonly used as excipients in human parenteral formulations can provide the level of ionic strength needed to prevent AAV2 vector aggregation when used at isotonic concentrations." This reveals that these specific multivalent ions are known, used in parenteral formulations, and their ability to generate ionic strength is recognized.
5. pH Dependence of Aggregation: Qu, G. et al. (2003) reported that AAV2 vector aggregation is pH dependent.

Obviousness Argument and Motivation to Combine:

A person of ordinary skill in the art (POSA) in the field of AAV vector formulation, at the time of the invention, would have been acutely aware of the challenge of AAV aggregation at high concentrations, as documented by Huang (2000) and Xie et al. (2004). This problem led to significant losses during purification, inconsistencies in testing, and limitations in in vivo administration.

The teachings of Xie et al. (2004) would have guided a POSA to explore the use of "elevated concentrations of salt" to prevent this aggregation. However, for therapeutic applications, the POSA would also be constrained by the need for isotonic formulations, particularly for in vivo administration, as acknowledged in the patent.

Given these two known requirements (high salt for stability, isotonicity for in vivo use), a POSA would turn to fundamental principles of solution chemistry and pharmaceutical formulation. Basic chemistry dictates that multivalent ions contribute more significantly to ionic strength for a given molar concentration compared to monovalent ions, thus offering a pathway to achieve high ionic strength without excessive osmolarity. The patent itself confirms that "salts of sulfate, citrate, and phosphate... are commonly used as excipients in human parenteral formulations". Therefore, a POSA would have a clear motivation to combine the teaching of using "elevated salt concentrations" (Xie et al., 2004) with the use of these commonly known multivalent ionic excipients to create a high ionic strength, yet isotonic, solution.

The specific ionic strength of "greater than 200 mM" as a threshold for preventing aggregation, while a valuable finding, is demonstrated in the patent's own FIG. 1B to be a general effect regardless of the specific salt. A POSA, motivated to find an effective "elevated salt concentration," would arrive at such a threshold through routine experimentation using the identified multivalent salts. Similarly, the pH range of 7.5 to 8.0 would be a matter of routine optimization, especially given the established understanding of AAV aggregation's pH dependence (Qu et al., 2003).

Therefore, the combination of:

1. Xie et al. (2004), teaching the need for elevated salt concentrations to prevent AAV aggregation at high vector concentrations.
2. General knowledge in pharmaceutical formulation, emphasizing the importance of isotonicity for in vivo administration.
3. Fundamental chemical principles, demonstrating that multivalent ions achieve higher ionic strength more efficiently than monovalent ions, thus facilitating isotonicity.
4. The patent's own acknowledgment that citrate, sulfate, and phosphate are commonly used multivalent excipients in human parenteral formulations.
5. Qu et al. (2003), highlighting the pH dependence of AAV aggregation, motivating routine pH optimization.

would have rendered the claimed composition of Claim 1 obvious to a POSA. The POSA would have been motivated to combine these known elements and approaches to solve the recognized problem of AAV aggregation in high-concentration, therapeutically relevant formulations, arriving at the claimed solution through predictable steps of optimization.