HPB & Philo

HPB, in the glossary of the Key, apparently consulting a bio on Philo, considers his writings to be of a kabbalistic nature - 

Philo-Judaeus. A Hellenized Jew of Alexandria, a famous historian and philosopher of the first century, born about the year 30 B. C., and died between the years 45 and 50 A. D. Philo's symbolism of the Bible is very remarkable. The animals, birds, reptiles, trees, and places mentioned in it are all, it is said, "allegories of conditions of the soul, of faculties, dispositions, or passions; the useful plants were allegories of virtues, the noxious of the affections of the unwise and so on through the mineral kingdom; through heaven, earth and stars; through fountains and rivers, fields and dwellings; through metals, substances, arms, clothes, ornaments, furniture, the body and its parts, the sexes, and our outward condition." (Dict. Christ. Biog.) All of which would strongly corroborate the idea that Philo was acquainted with the ancient Kabbala. 

Although the explanations given are brief and from indirect sources, the difficult to prove theory that Philo was aware of the Kabbalah, which not even many Kabbalists of her time would support, actually is slowly gaining mainstream credibility:

Naomi G. Cohen, Philo’s Cher. 40–52, Zohar III 31a,
and BT Hag. 16a, Journal of jewish studies, vol. lvii, no. 2, autumn 2006

It has been shown that Philo has culled this esoteric tradition from a commentary
identified by him as ‘Jeremiah’, since as pointed out above, while
Philo names Jeremiah in II Cher. §49, what he is obviously quoting is an esoteric
commentary on the prophetic verse found in the Book of Jeremiah, for
in the same section he also identifies the esoteric exegesis of the Pentateuch as
belonging to Moses.

The passage from the Zohar contains similar ideas, projects similar images,
and uses the same biblical text, in the form found in the Septuagint and
in Philo, but not in the MT, and BT Hagiga 16a contains desiccated ‘bare
bones’ of this construct, divested of any discernable theosophical dimension.
Thus the very same midrashic building blocks which stem from the Septuagint
reading of Jer. 3:4 appear in Philo and in the Zohar, and to some extent
in BT Hagigah 16a as well. The completely different form that the tradition
takes in these very different sources is apparently the result of their having
been transplanted into very different cultural soils and climates.

This supports the thesis that a pool of esoteric Midrash common to the
Hebrew/Aramaic tradition and the Greco-Jewish ‘world’ existed in the days of
the Second Temple—in the days of Philo who was more or less contemporary
with Hillel and Shammai. Further, since as we have seen, this specific tradition
must have originated in Hellenistic Jewish circles for whom theHoly Scripture
was the Septuagint, it also shows that contributions to this midrashic pool
came not only from sources that originated in the Hebrew/Aramaic speaking
communities, but that this was at least sometimes a two way street.59 And
finally, it also lends support for the hypothesis, which, after a half-century
of almost total eclipse, in recent years is gaining a more and more serious hearing in scholarly circles, that some very early esoteric traditions are in fact
embedded in the Zohar.